Z- P. METCALI
LIBRARY OF
1885- IQ56
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c
4.
ENTOMOLOGY
FOLSOM
ENTOMOLOGY
WITH SPECIAL REFERENCE TO
ITS ECOLOGICAL ASPECTS
BY
JUSTUS WATSON FOLSOM, Sc.D. (Harvard)
ASSISTANT PROFESSOR OF ENTOMOLOGY AT THE UNIVERSITY OF ILLINOIS
THIRD REVISED EDITION
WITH FIVE PLATES AND 308 TEXT-FIGURES
PHILADELPHIA
P. BLAKISTON'S SON & CO.
1012 WALNUT STREET
Copyright, 1922, by P. Blakiston's Son & Co.
P R I NTED IN U. S
THE MAPLE PRESS
PREFACE
This book gives a comprehensive and concise account of insects.
Though planned primarily for the student, it is intended also for the
general reader.
The book was written in an effort to meet the growing demand for a
biological treatment of entomology.
The existence of several excellent works on the classification of
insects (notably Comstock's Manual, Kellogg's American Insects and
Sharp's Insects) has enabled the author to omit the multitudinous
details of classification and to introduce much material that hitherto
has not appeared in text-books.
As a rule, only the commonest kinds of insects are referred to in the
text, in order that the reader may easily use the text as a guide to per-
sonal observation.
All the illustrations have been prepared by the author, and such as
have been copied from other works are duly credited.
To Dr. S. A. Forbes the author is especially indebted for the use of
literature, specimens and drawings belonging to the Illinois State
Laboratory of Natural History.
Permission to copy several illustrations from Government publica-
tions was received from Dr. L. O. Howard, Chief of the Bureau of Ento-
mology; Dr. C. Hart Merriam, Chief of the Division of Biological
Survey, and Dr. Charles D. Walcott, Director of the U. S. Geological
Survey. Several desired books were obtained from F. M. Webster,
of the Bureau of Entomology.
Acknowledgments for the use of figures are due also to Dr. E. P.
Felt, State Entomologist of New York; Dr. E. A. Birge, Director of the
Wisconsin Geological and Natural History Survey; Prof. E. L. Mark
and Prof. Roland Thaxter, of Harvard University; Prof. J. H. Comstock
of Cornell University; Prof. C. W. Woodworth of the University of
California; Prof. G. Macloskie of Princeton University; Prof. W. A.
Locy of Northwestern University; Prof. J. G. Needham of Cornell Uni-
versity; Dr. George Dimmock of Springfield, Mass.; Dr. Howard Ayers
of Cincinnati, Ohio; Dr. W. M. Wheeler of the American Museum of
Natural History, New York City; Dr. W. L. Tower of the University
of Chicago; Dr. A. G. Mayer, Director of the Marine Biological Lab-
oratory, Tortugas, Fla.; James H. Emerton of Boston, Mass.; Dr. and
V
VI PREFACE
Mrs. G. W. Peckham of Milwaukee, Wis.; Dr. William Trelease,
Director of the Missouri Botanical Garden; Dr. Henry Skinner, as
editor of "Entomological News;" and the editors of "The American
Naturalist."
Acknowledgments are further due to the Boston Society of Natural
History, the American Philosophical Society and the Academy of
Science of St. Louis.
Courteous permission to use certain figures was given also by The
Macmillan Co.; Henry Holt & Co.; Ginn & Co.; Prof. Carl Chun of
Leipzig; F. Diimmler of Berlin, publisher of Kolbe's Einfiihrung; and
Gustav Fischer of Jena, publisher of Hertwig's Lehrbuch and Lang's
Lehrbuch.
The first edition, which was translated into Japanese by Professors
Miyake and Uchida, has had a large sale in Japan.
The second edition contained much new matter, particularly a
chapter on the transmission of diseases by insects.
This third edition has been brought up to date by ^he addition of a
great deal of new material, including a few new illustrations. Some two
hundred and fifty titles have been added to the bibliography but, to
accommodate these, it was necessary to discontinue other titles of less
importance.
A new chapter, on insect ecology, is given. This ought to prove
useful, as the literature of the subject is scattered, and there has been
no similar comprehensive treatment of ecology from the viewpoint of
the entomologist.
In the preparation of this chapter the author has been fortunate in
having the expert advice of Professor V. E. Shelford, of the University
of Illinois; who is not responsible, however, for any possible short-
comings in the chapter.
The following scientific men also have gladly assisted by giving
desired information: — Dr. L. O. Howard, chief of the Bureau of Ento-
mology; Mr. A. F. Burgess, of the Bureau of Entomology; Prof. J. H.
Comstock, Cornell University; Prof. A. F. Shull, University of Michi-
gan; Mr. Nathan Banks, Museum of Comparative Zoology, Cambridge,
Mass.; Mr. Charles Macnamara, Arnprior, Ontario, Canada; Professor
A. O. Weese, University of New Mexico; Dr. C. P. Alexander, Mr. W. P.
Flint and Dr. H. Yuasa, of the Illinois State Natural History Survey;
Professor A. D. MacGillivray and Dr. R. D. Glasgow, of the Univer-
sity of Illinois.
Permission to use the map for Plate V. was courteously given by
Dr. B. E. Livingston and the Carnegie Institution of Washington.
CONTENTS
Chapter Page
I. Classification ' i
II. Anatomy and Physiology 27
III. Development 129
IV. Adaptations of Aquatic Insects 165
V. Color and Coloration 172
Vl. Adaptive Coloration 194
VII. Insects in Relation to Plants 212
VIII. Insects in Relation to Other Animals 233
IX. Transmission of Diseases by Insects 248
X. Interrelations of Insects 270
XL Insect Behavior 302
XII. Distribution 322
XIII. Insect Ecology 348
XIV. Insects in Relation to Man 410
Literature 430
Index 479
ENTOMOLOGY
CHAPTER I
CLASSIFICATION
At tJie outset it is essential to know where insects stand in relation to
other animals.
Arthropoda. — Comparing an insect, a centipede and a crayfish
with one another, they are found to have certain fundamental characters
in common. All are bilaterally symmetrical, are composed of a linear
series of rings, or segments, bearing paired, jointed appendages, and
have an external skeleton, consisting largely of a peculiar substance
known as chitin.
If the necessary dissections are made, it can be seen that in each of
these types the alimentary canal is axial in position; above it extends
Fig. 1. — Diagram to express the fundamental structure of an arthropod, a, antenna;
al, alimentary canal; b, brain; d, dorsal vessel; ex, exoskeleton; I, limb; n, nerve chain; s,
subcesophageal ganglion. — After Schmeil.
the dorsal blood vessel and below Hes the ventral ladder-like series of
segmental ganglia and paired nerve cords, or commissures; between the
commissures that connect the brain and the subcesophageal ganglion
passes the oesophagus. These relations appear in Figs, i and 165.
Furthermore, the sexes are almost invariably separate and the primary
sexual organs consist of a single pair.
No animals but arthropods have all these characters, though the
segmented worms, or annelids, have some of them^ — for example the
segmentation, dorsal heart and ventral nervous chain. On account of
these correspondences and for other weighty reasons it is believed that
I
ENTOMOLOGY
arthropods have descended from annelid-Hke ancestors. Annelids,
however, as contrasted with arthropods, have segments that are essen-
tially ahke, have no external skeleton and never have paired limbs that
are jointed.
Classes of Arthropoda. — Excluding the king-crab, trilobites and a
few other forms that have no im-
mediate entomological importance,
the remaining arthropods fall into nine
classes, which are characterized as
follows :
Crustacea. — Aquatic, as a rule.
Head and thorax often united into a
cephalo thorax. Numerous paired
appendages, typically biramous (Y-
shaped) ; abdominal limbs often pres-
ent. Two pairs of antennae.
Respiration branchial (by means of
gills) or cutaneous (directly through
the skin). The exoskeleton contains
carbonate and phosphate of lime in
addition to chitin. Example, crayfish.
Arachnida. — Terrestrial. Usually
two regions, cephalothorax and abdo-
men; though various Acarina have but
one and Solpugida have all three— head,
thorax and abdomen. Cephalothorax
unsegmented, bearing two pairs of oral
Natural appendages and four pairs of legs.
Eyes simple. Abdomen segmented or
not, limbless. Respiration tracheal, by means of book-leaf tracheae,
tubular tracheae, or both; stigmata almost always abdominal, at
most four pairs. Heart abdominal in position. Example, Buthus
(Fig. 2).
Onychophora. — Terrestrial. Vermiform (worm-like), unsegmented
externally. One pair of ringed antennae, a pair of jaws and a pair of
oral shme papillae. Legs numerous, paired, imperfectly segmented.
Respiration by means of short tubular tracheae, the stigmata of which
are scattered over the surface of the body, or arranged in rows. Genital
opening posterior. Numerous nephridia (excretory) are present,
arranged segmentally in pairs. Two separate longitudinal nerve cords.
-A scorpion, Buthus.
size.
CLASSIFICATION 3
connected by transverse commissures. Integument delicate. Some
fifty species are known. Example, Peripatus (Fig. 3).
Diplopoda. — Terrestrial. Two regions, head and body. Body
usually cylindrical, with numerous segments, most of which are double
and bear two pairs of short limbs, which are inserted near the median
ventral line. Eyes simple, antennae short, usually seven-segmented,
Fig. 3. — Peripatus capensis. Natural size. — After Moseley.
mouth parts consisting of a pair of mandibles and a compound plate,
or gnathochilarium. Genital openings separate, anterior in position
(on the second segment of the body). Example, Spirobolus (Fig. 4)..
Pauropoda. — Terrestrial. Two regions, head and body. Body
elongate, twelve-segmented, with nine pairs of functional legs; each of
the first five apparent terga consists morphologically of two united
terga. Eyes absent, but a pair of eye-like spots may be present.
Antennas characteristic; with four proxi-
mal segments and a pair of distal
branches bearing three filaments in all.
Mouth parts represented by mandibles,
maxillae (?) and labium (?). A single
genital opening (female) or a pair of
openings (male) on the third body
segment. Minute arthropods, at most
about one millimeter in length. Example,
Pauropus.
Chilopoda. — Terrestrial. Two regions,
head and body. Body long and flat-
tened, with numerous segments, each of
which bears a pair of long six- or seven-
segmented limbs, which are not inserted near the median line. Eyes
simple and numerous (agglomerate in Scutigera) antennae long, many-
segmented. A pair of mandibles and two pairs of maxillae. A single
genital opening, on the preanal segment. Example, Scolopendra (Fig. 5) .
Symphyla. — Terrestrial. Two regions, head and body. Head
prognathous, with a Y-shaped epicranial suture. Eyes few. Antennae
long, multiarticulate. Four pairs of mouth parts; mandibles two-
FiG. 4. — A diplopod, Spirobolus
marginatus. Natural size.
4 ENTOMOLOGY
segmented. Body elongate, with fifteen distinct terga, and eleven or
twelve pairs of legs. Cerci well developed. Genital opening in the
third body segment. One pair of spiracles, opening on the head, under
the antennae. Small arthropods not more than five or six millimeters
in length. Example, Scolopendrella (Fig. 6).
Mjrrientomata. — Terrestrial. Three regions: head, thorax and
abdomen. Head small, conical, prognathous. One pair of eye-like
spots. Antennae absent. Mouth parts suctorial. Mandibles and
maxillae attenuate, styliform, protrusible and retractile. Labium
attenuate. Body strongly elongate, fusiform, narrowing posteriorly,
fifteen-segmented in adults. Thorax distinct from abdomen; prothorax
shorter than meso- or metathorax. Three pairs of thoracic legs, and a
pair of vestigial legs on each of the first three abdominal segments.
Last four abdominal segments more or less retractile. Cerci absent.
Genital opening posterior. Male genitalia elongate, retractile, distally
bilobed, with a pair of slender, forceps-like appendages. Female appen-
dage short, with short forceps. Minute delicate arthropods, seldom
more than one millimeter in length. Example, Acerentomon (Fig. 8.)
A single order, Protura, discovered and named by Silvestri, and
consisting of two families: Acerentomidae, without a tracheal system,
and Eosentomidae, with simple tracheae and two pairs of thoracic
spiracles. Protura, easily overlooked on account of their small size, are
doubtless widely distributed. At present twelve species are known from
Europe and twelve from the United States, all but one of our species
having been described by Dr. H. E. Ewing.
Insecta (Hexapoda). — Primarily terrestrial. Three distinct regions
— head, thorax and abdomen. Head with a pair of compound eyes in
most adults, one pair of antennae and typically three pairs of mouth
parts — mandibles, maxillae and labium — besides which a hypopharynx,
or tongue, is present. In Apterygota a fourth pair of mouth parts is
associated with the hypopharynx. Thorax with a pair of legs on each
of its three segments and usually a pair of wings on each of the posterior
two segments; though there may be only one pair of wings (as in Diptera,
male Coccidae and male Strepsiptera) ; the prothorax never bears wings.
Abdomen typically with eleven segments and without legs, excepting in
some larvae (as those of Lepidoptera, Tenthredinidae and Panorpidae).
Stigmata paired and segmentally arranged. A metamorphosis (direct
or indirect) occurs except in Thysanura and Collembola.
Relationships. — The interrelationships of the classes of Arthropoda
form an obscure and highly debatable subject.
CLASSIFICATION
5
Crustacea and Insecta agree in so many morphological details that
their resemblances can no longer be dismissed as results of a vague
''parallelism," or "convergence" of development, but are inexplicable
except in terms of community of origin, as Carpenter has insisted.
Arachnida are extremely unhke other arthropods but find their
nearest allies among Crustacea, particu-
larly the fossil forms known as trilobites.
Onychophora, as represented by Peri-
patus, are often spoken of as bridging the
gulf that separates Insecta, Chilopoda and
Diplopoda from Annelida. Peripatus in-
deed resembles the cha^topod annelids in
its segmentally arranged nephridia, der-
momuscular tube, coxal glands and soft
integument, and resembles the three other
classes in its tracheae, dorsal vessel with
paired ostia, lacunar circulation, mouth
parts and salivary glands. These resem-
blances are by no means close, however,
and Peripatus does not form a direct link
between the other tracheate arthropods
and the annelid stock, but is best regard-
ed as an offshoot from the base of the
arthropodan stem.
In speaking of annelid ancestors, none
of the recent annelids are meant, of course,
but reference is made to the primordial
stock from which recent annelids them-
selves have been derived.
Though Diplopoda and Chilopoda have
long been grouped together under the name
Myriopoda, they really have so little in
common, beyond the numerous limb-bearing segments and the charac-
ters that are possessed by all tracheate arthropods, that their differences
entitle them to rank as separate classes. Chilopoda as a whole are
more nearly related to Insecta than are Diplopoda, as regards seg-
mentation, mouth parts, tracheae, genital openings and other characters.
Scolopendrella, now placed in a class by itself, Symphyla, presents a
remarkable combination of diplopodan and insectean characters.
Scolopendrella (Fig. 6) and the thysanuran Campodea have the same
Fig. s. — A centipede, Scolopen-
dra heros. About two-thirds the
maximum length.
ENTOMOLOGY
kind of head, with long moniliform antennae, and agree in the general
structure of the mouth parts; the number of body segments is nearly
the same, the legs and claws are essentially alike, and cerci and paired
abdominal stylets are present in the two genera, not to mention the
Fig. 6. — Section of Scolopendrella immaculata, b, brain; c, coxal gland; /, fore intes"
tine; h, hind intestine; m, mid-intestine; n, nerve chain; o, opening of silk gland; od, oviduct;
ov, ovary; s, silk gland; u, urinary tube. — After Packard.
correspondences of internal organization. Indeed, it is highly prob-
bable, as Packard maintained, that the most primitive insects, Thysa-
nura (and consequently all other insects), originated from a form much
like Scolopendrella. A singular thysanuran, Anajapyx vesiculosus
(Fig. 7) was discovered by Silvestri, who regarded
it as being in many respects the most primitive in-
sect known, combining as it does characters of
Symphyla, Diplopoda and Campodea.
Silvestri discovered also a peculiar arthropod,
Acerentomon doderoi (Fig. 8) for which he made a
new order — Protura. Berlese added two genera to
this order, namely, Eosentomon and Acerentulus ; and
according to good authority Protapteron indicum
Schepotieff belongs to the former genus. Silvestri,
followed by Borner, put Protura among Aptery-
gota; but Berlese, who grouped these forms under
the name of Myrientomata, found that they had
myriopodan as well as insectean affinities; and
Rimsky-Korsakow argued that Myrientomata
cannot be rightly regarded as insects, but logically
constitute a class by themselves; and that this class
does not form a direct link between myriopods and
insects, but that all these groups came from the same ancestral
stock. Protura have actually little in common with insects; the pecu-
liar structure of the mouth parts and genitalia excluding them from
the group Apterygota.
Fig. 7. — Anajapyx
vesiculosus. Length, 2
mm. — After Silvestri.
CLASSIFICATION
The following diagram (Fig. 9) expresses very crudely one view as
to the annelid origin of the chief classes of Arthropoda.
The naturalness of the phylum Arthropoda was questioned by
Kingsley and Packard. The latter author divided Arthropoda into
five independent phyla, holding that "there was no common ancestor
of the Arthropoda as a whole, and that the group is a polyphyletic one."
This iconoclastic view, however, by emphasizing unduly the structural
differences among arthropods, tends to conceal the
many deep-seated resemblances that exist between the
classes of Arthropoda.
Carpenter, in a most sagacious summary of the
whole subject of arthropod relationships, brought to-
gether no little evidence in favor of a revised form of
the old Miillerian theory of crustacean origins. He
traced all the classes of Arthropoda back to com-
mon arthropodan ancestors with a definite number
of segments and distinctly crustacean in character;
then traced these primitive arthropods back to forms
like the nauplius larva of Crustacea, and these in turn
to a hypothetical form like the trochosphere larva of
recent polychaete annelids.
Orders of Insects. — Linnaeus arranged insects in
seven orders, namely, Coleoptera, Hemiptera, Lepi-
doptera, Neuroptera, Hymenoptera, Diptera and
Aptera. The wingless insects termed Aptera were
soon found to belong to diverse orders and the name
has become so ambiguous as to meet with little
approval.
From theLinnsean group Hemiptera, the Or thoptera Length, i.28nim.—
, , 1 XT 1 After SiLVESTRi.
were set apart the old order Neuroptera a heteroge-
neous and unnatural group, was split into several distinct orders, and
many other changes in the classification were necessary.
Without entering any further into the history of the subject, it is
sufficient to say that increasing discrimination on the part of entomolo-
gists has been followed by a gradual increase in the number of orders.
Naturally, the systems of classification have grown and changed
considerably, keeping pace with increasing knowledge.
Brauer (1885) made such important contributions to the subject that
his system, modified more or less by Packard, Comstock and others,
has been followed for almost forty years.
Pig. 8. — Aceren-
tomon doderoi.
8 ENTOMOLOGY
Handlirsch has made the most exhaustive investigation of the phylo-
geny of the major groups of insects. His revolutionary system, which
is based upon fossil as well as recent forms, is of the kind to which one
applies the term "epoch-making," but is unfortunately so erratic and
fantastic in some respects that it has not been generally adopted.
As the orders of insects have evolved from one another in many
different directions, like the branches of a tree, their natural relation-
ships can not be expressed correctly in any linear sequence, like that
of this book. Here the orders are listed approximately according to
the degree of specialization, beginning with the most primitive insects;
INSECTA
CRUSTACEA \ .CHILOPODA
\ symphylaA/^diplopoda
arachnidaX /
^
/
^MAUGOPODA
ARTHR
jpooj^ ANNELIDA
Fig. 9. — Diagram to indicate the origin of classes of Arthropoda.
and the attempt is made to group together orders that are nearly
related to one another.
In the course of the following synopsis of the orders of insects it is
necessary to use some terms, as metamorphosis and thysanurijorm, in
anticipation of their subsequent definition.
I. Thysanura. — No metamorphosis. Eyes aggregate, compound
or absent. Antennae long, filiform, multiarticulate. Mouth parts
mandibulate, either free (ectognathous) or enclosed in the head {ento-
gnathous). Wings invariably absent. Thoracic segments simple
and similar; prothorax well developed. Abdomen usually elongate,
with ten evident segments and often traces of an eleventh segment;
with two to eight pairs of rudimentary limbs, or styli, often accompanied
by eversible ventral sacs. Cerci usually long, filiform, multiarticulate,
with frequently a similar median pseudocercus; but sometimes with
CLASSIFICATION 9
few segments (Anajapyx) or represented by a pair of forceps (Japyx).
Integument thin; scales present or absent. Active and terrestrial,
"bristletails." Examples, Campodea (Fig. lo), Japyx, Machilis,
Lepisma (Fig. ii), Anajapyx (Fig. 7). Some three hundred species are
known.
2. Collembola. — No metamorphosis. Eyes ocelliform, not more
than eight on each side, often fewer in number or absent. Antennae
short, of four segments in most genera; five or six in a few genera.
Mouth parts entognathous and typically mandibulate, with occasional
secondary suctorial modifications. Wings invariably absent. Tho-
FiG. 10. — Campodea. Length, 3 mm. FiG. 11. — Lepisma. Length, 10 mm.
racic segments simple and similar, or prothorax reduced. Body cylin-
drical or globular. Ventral tube and furcula usually present, sometimes
rudimentary. Integument delicate; scales present in some genera.
Small or minute terrestrial insects, "springtails. " Examples, Acliorutes
(Fig. 12), Sminthurus (Fig. 13). About nine hundred species have
been described.
Under the term Apterygota the Thysanura and Collembola, as primi-
tively wingless insects, are conveniently distinguished from all other
insects, or Pterygota.
3. Orthoptera. — Metamorphosis direct. Eyes well developed.
Antennae usually filamentous, shorter or much longer than the body,
multiarticulate. Mouth parts mandibulate. Pronotum usually large
ENTOMOLOGY
(small in Phasmidae). Wings two pairs as a rule, though not infre-
quently reduced or absent. Fore wings coriaceous (leathery, forming
tegmina); hind pair membranous, ample, closely reticulate, plicate
along the numerous radiating principal veins.
Abdomen with ten evident segments and traces of
eleven or twelve. Cerci one- to eight-segmented.
Terrestrial and mostly phytophagous. Seven
families: Blattidae, Mantidae Gryllidae, Grylloblat-
tidae, Tettigoniidae (formerly Locustidae), Locus-
tidae (formerly Acridiidae, Fig. 14), Phasmidae (Fig.
243). More than ten thousand species are known.
4. Dermaptera.— Metamorphosis direct. Eyes
facetted, reduced, or absent. Antennae long, filiform,
with ten to fifty segments in adults. Mouth parts
mandibulate, prognathous; lingua and superlinguae
well developed; labium split to the mentum; para-
glossa united with glossa of same side. Prothorax
large. Thoracic segments distinct. Tarsi three-
segmented. Elytra short, 'scale-like, meeting in a
straight line. Wings projecting from under the
elytra, ear-shaped, with many radiating principal
veins, folding plicately, also twice transversely.
Abdomen with eleven segments, the tergites and
sternites strongly and complexly imbricate laterally, with a terminal
pair of forceps (cerci). Wingless species numerous. Some four hun-
dred species are at present known.
Three suborders, each represented by one family : Arixeniidae (one
species) ; Hemimeridae, containing
a single African species (Fig. 15),
which is flattened, eyeless, wing-
less, with long unsegmented cerci,
viviparous, and parasitic on the rat;
and Forficulidae, formerly a family
of Orthoptera.
5. Platyptera. — Metamorphosis
direct. Mouth parts mandibulate.
Wings, if present, two pairs, delicate,
membranous, equal or hind pair smaller, and with the principal veins
few and simple. Abdomen with usually ten evident segments and
often traces of an eleventh. Integument usually thin. Nymphs thy-
sanuriform. Five suborders.
Fig. 12. — The snow
&ea, Achorutes nivicola.
Length, 2 mm.
Sminlhiiriis hortensis. Length,
1.2 mm.
CLASSIFICATION
Suborder Isoptera. — Eyes facetted, vestigial or absent. Antennae
long and filamentous or short and moniliform, nine- to thirty-one-
FiG. 14. — Schistocerca americana. Slightly re-
duced.
Fig. 15. — Hemimerus talpoides. Length,
1 1.5 mm. — After Hansen.
segmented. Mouth parts prognathous or hypognathous.^ Thoracic
segments simple, similar and equal ; pro thorax large, free. Tarsi four- or
five-segmented. Alate or apter-
ous. Wings elongate, similar,
equal, membranous, dehcate, with
few veins, sometimes with an in-
deffnite reticulation, with a char-
acteristic basal suture a ong which
the wing breaks off; hind wings not
folded. Abdomen elongate, wieh
ten segments and a pair of short
two- to six-segmented eerie In-
tegument weak. Social in habit
and polymorphic; known as white
ants. Example, Termes (Fig.
28o)Aboutonethousanddescribedspecies.
Suborder Embioptera. — Eyes facetted. Antennae with fifteen to
thirty-one or more segments. Mouth partsprognathous; with a labial
^Prognathous, directed forward, hypognatJwus, directed downward.
Fig. 16. — Oligotoma michaeli. Length 10.5
mm. — After McLachlan.
ENTOMOLOGY
Fig.
Psocus venosus. Length, 5 mm.
spinneret. Thorax elongate; pro thorax small. Tarsi three-segmented.
Wings (sometimes absent) two pairs, elongate, similar, equal, mem-
branous, delicate, with few and feebly developed longitudinal and cross
veins; not folded. Abdomen elongate, with ten segments and frequent-
ly an eleventh tergite, and a pair of short stout biarticulate cerci.
Integument delicate. Feeble insects,
not social in habit. Examples,
Embia, Oligotoma (Fig. i6). Some
twenty species, all from warm
climates.
Suborder Zoraptera. — Eyes ves-
tigial or absent. Antennse monili-
f orm, nine-segmented. Thorax long,
as long as the abdomen; prothorax large, larger than the meso- and
metathorax combined. Tarsi two-segmented. Apterous, or with two
pairs of wings; the fore wings with a few irregular veins and cells.
Abdomen with ten evident segments; the tenth and eleventh united
dorsally. Cerci short, one -segmented. Minute, active forms (little
more than two millimeters in length), terrestrial,
predaceous. One genus, Zorotypus, represented
by three Oriental species (Africa, Ceylon, Java),
one species from Costa Rica and two from the
United States.
These insects are most nearly related to Isop-
tera and Corrodentia.
Suborder Corrodentia.^Eyes facetted. An-
tennae filiform, with thirteen to fifty or more
segments. Mouth parts hypognathous. Pro-
thorax reduced. Tarsi two- or three-segmented.
Wings present, rudimentary or absent; fore pair the
larger; veins few and irregular. Abdomen short
and stout, with nine or ten segments. Cerci absent.
Integument delicate. Small terrestrial insects,
including the book lice and other psocids.
Example, Psocus (Fig. 17). More than two hundred species are
known.
Suborder Mallophaga.^Small wingless flattened insects of parasitic
habit. Head large. Eyes of a few isolated ocelli, or vestigial, or
absent. Antennae three- to five-segmented. Mouth parts prognathous.
Prothorax distinct; mesothorax often, and metathorax usually, trans-
FiG. 18.— A
louse, Menopon.
2 mm.
CLASSIFICATION
13
ferred to the abdominal region. Tarsi one- or two-segmented. Abdomen
usually short and broad, eight- to ten-segmented. Cerci absent.
A B
Fig. 19. — Pteronarcys regalis. A, nymph (after Newport); B. imago. Slightly reduced.
Fig. 20. — Hexagenia variabilis. A, nymph; B, imago. Natural size.
Biting lice, or bird Hce, parasitic on birds and a few mammals, feeding
on feathers, hair or skin. Example, Menopon (Fig. 18). More than
fifteen hundred species have been described.
14
ENTOMOLOGY
6. Plecoptera. — Metamorphosis direct. Antennae filiform, long,
multiarticulate. Mouth parts mandibulate. Prothorax large. Wings
Fig. 21. — Libellula pulchella. A, last nymphal skin; B, imago. Slightly reduced.
two pairs, membranous, coarsely and complexly reticulate; equal or
else hind wings larger and with an ample plicate anal area. Abdomen
with ten segments and usually
a pair of long multiarticulate
cerci. Integument soft.
Nymphs thysanuriform,
aquatic; adults unique in
having tracheal gills. The
stone-flies. Example, Ptero-
narcys (Fig. 19). A single
family, Perlidae, comprising
two hundred species.
7. Ephemerida.— Meta-
morphosis direct. Antennae
bristle-like. Mouth parts
mandibulate, but atrophied
in the adult. Prothorax
small. Wings membranous, minutely reticulate; hind pair much the
smaller, rarely absent. Abdomen slender, with ten segments and three
or two very long multiarticulate caudal filaments (a pair of cerci, with
of ten a median pseudocercus) . Integument delicate. Nymphs thysa-
nuriform, aquatic, with lateral gills. May-flies, or sand-flies. Exam-
ple, Hexagenia (Fig. 20). Three hundred species.
8. Odonata. — Metamorphosis direct. Head mobile; eyes large.
Antennas inconspicuous, bristle-shaped. Mouth parts mandibulate.
Prothorax small, free; meso- and metathorax intimately united.
Tarsi three-segmented. Wings four, elongate, subequal, similar, mem-
FiG. 22. — Euthrips tritici. Length, 1.2 mm.
CLASSIFICATION
15
branous, minutely reticulate, with characteristic costal joint (nodus),
arculus and triangle. Abdomen slender, with ten segments. Cerci
one-segmented. Nymphs aquatic; adults predatory. Dragon-flies
Fig. 23. — Benacus griseus. Slightly reduced.
Fig. 24. — Head louse,
Pediculus capitis, female.
Length, 2 mm.
and damsel -flies. Example, Lihellula (Fig. 21). About two thousand
species have been described.
Fig. 25. — Hydrophilus triangularis. Natural size.
9. Thysanoptera. — Metamorphosis direct, but including a subpupal
stage. Eyes well developed. Mouth parts suctorial, in part asym-
metrical. Prothorax long, free. Tarsus one- or two-segmented, ter-
i6
ENTOMOLOGY
Fig. 26.— Chrysopa
plorabunda. Slightly
reudced.
minating in a bladder -like organ. Wings present, rudimentary or
absent, the two pairs narrow, equal, similar, with few or no veins and
fringed with long hairs. Abdomen with ten segments. Minute, slender
insects, known as "thrips." Example, Euthrips (Fig. 22). About
two hundred species have been described.
10. Hemiptera. — Metamorphosis direct. Antennae usually few-
segmented. Mouth parts suctorial. Prothorax usually large. Wings
usually present, except in the parasitic forms.
Eighteen thousand species. Two suborders.
Suborder Homoptera. — Head deflexed. Wings
four, sloping roof -like, similar and membranous
or fore pair somewhat coriaceous (leathery)
throughout. Wings absent in female Coccidae; in
males, fore wings present, hind wings absent,
represented by halteres. Phytophagous insects.
Example, Cicada (Fig. 209). Six thousand species.
Suborder Heteroptera. — Head free, not deflexed. Antennas often
long, few-segmented. Prothorax free. Wings four (sometimes reduced
or absent) folded flat; fore wings thickened basally, membranous
apically (hemelytra) , overlapping obliquely; hind wings membranous,
with large anal area. Terrestrial or
aquatic. The true "bugs." Example,
Benacus (Fig. 23) . About twelve thousand
species.
11. Parasita.^ — Metamorphosis direct.
Wingless parasites. Eyes simple or absent.
Antennae short, three- to five-segmented.
Prognathous. Head with a short tubular
beak, crowned with hooks, containing
a delicate protrusible sucking tube. Tho-
racic segments intimately united. Tarsus
with a single claw. Integument thin. The sucking lice, blood-sucking
parasites of mammals, represented by the " cooties." Example, Pedicu-
lus (Fig. 24). Some fifty species are known.
12. Coleoptera. — Metamorphosis indirect. Ocelli usually absent.
Antennae of various forms, with segments varying in number (two to
twenty-seven) but commonly ten or eleven. Mouth parts mandibulate.
Prothorax large, free. Two pairs of wings ; fore pair horny or shell-hke as
1 Various names have been used for this group, but the name which has priority and
is sanctioned by longest usage is Farasiia (Latreille, 1796).
Fig. 27. — Bittacus slrigosus. Nat-
ural size.
CLASSIFICATION
17
a rule {elytra), meeting in a straight line; hind pair membranous, often
folded. Larvae sometimes thysanuriform, often eruciform, mandibulate.
Hard-bodied iusects, the beetles. Example, Hydrophiliis (Fig. 25).
About one hundred and fifty thousand species.
13. Strepsiptera. — Hypermetamorphic; first larva hexapodous, with
long anal stylets; later larvae apodous, degenerate. Female legless,
larviform, larviparous, with no pupal stage; male pupa hymenopteroid,
within a puparium. Male with large eyes; antennae seven- to four-seg-
mented, flabellately produced; labrum and labium absent; mandibles
ensiform; maxillae palpiform, two- or three-segmented. Prothorax and
mesothorax greatly reduced; metathorax preponderant. One pair of
Fig. 28. — Molanna cinerea. A, larva; B, imago. X 4 diameters. — After Felt.
wings, the metathoracic, membranous, with only radial veins (eight to
five), folding longitudinally. Anterior wings reduced to balancers.
Abdomen ten-segmented. Integument thin and soft. Parasitic. About
two hundred species are known. Found in all regions of the world.
14. Neuroptera. — Metamorphosis indirect. Antennae conspicuous.
Mouth parts mandibulate. Prothorax large. Wings almost always
four, membranous, subequal or else hind pair smaller, complexly
reticulate, not plicate, without large anal area. Larvae thysanuriform
or in some cases eruciform, and aquatic or terrestrial, predaceous.
Example, lace-winged fly, Chrysopa (Fig. 26). About six hundred
species have been named.
15. Mecoptera. — Metamorphosis indirect. Antennae long, filiform.
Mouth parts mandibulate, at the end of a deflexed rostrum, or beak.
Prothorax small. Tarsi five-segmented. Wings four, elongate, mem-
l8 ENTOMOLOGY
branous, naked, coarsely reticulate, or else rudimentary or absent.
Larvae eruciform, caterpillar-like, with three pairs of thoracic legs and
often eight pairs of abdominal prolegs, carnivorous. Example, Bittacus
(Fig. 27). A single family, Panorpidae, comprising but few known species .
16. Trichoptera. — Metamorphosis indirect. Eyes prominent.
Antennae filiform. Mouth parts of imago rudimentary or imperfectly
suctorial; mandibles rudimentary or absent. Prothorax small. Tarsi
five-segmented. Wings four, membranous, hairy, veins moderate in
number, cross veins few; hind pair almost always the larger, with
pHcate anal area. Larvae suberuciform, with three pairs of thoracic
legs, aquatic, usually case-forming. Caddis worms and caddis flies.
Example, Molanna (Fig. 28). Between five and six hundred species
are known.
17. Lepidoptera. — Metamorphosis indirect. Antennae long, of vari-
ous forms, many-segmented. Mouth parts suctorial, mandibles absent
or rudimentary (except in a few generahzed species). Eyes well
developed. Ocelli sometimes present. Prothorax reduced. Tarsi
usually five-segmented. Wings four, large, similar, membranous, with
veins moderate in number, and few cross veins. Adults usually clothed
throughout with scales. Larvae eruciform (caterpillars), typically with
three pairs of thoracic legs and five pairs (sometimes fewer) of abdom-
inal prolegs, mandibulate, phytophagous (rarely carnivorous). Butter-
flies and moths. Some fifty thousand species have been described.
Two suborders, not sharply separated from each other.
Suborder Heterocera. — Antennae of various forms, but not ter-
minating in a distinct knob or club. Frenulum usually present.
Chiefly nocturnal in habit. Example, Callosamia (Fig. 239).
Suborder Rhopalocera.— Antennae simple, terminating in a distinct
club and without conspicuous lateral processes. Frenulum absent.
Diurnal normally. Examples, Papilio (Fig. 29), Anosia (Fig. 247, A).
18. Hymenoptera. — Metamorphosis indirect. Mouth parts at the
same time mandibulate and suctorial. Prothorax usually small. Tarsi
usually five-segmented. Wings two pairs, similar, membranous, trans-
parent or translucent, without scales, with a few irregular veins and
cells; venation sometimes reduced; hind wings smaller than fore wings;
fore and hind wings held together by a series of hooks {hamuli).
Abdomen usually with six or seven evident segments. Females with an
ovipositor, modified for sawing, boring or stinging. Larvae eruciform,
mandibulate; caterpillar-like, with head and legs, or maggot-like and
apodous. Twenty-five or thirty thousand species. Two suborders.
CLASSIFICATION
19
Suborder Terebrantia (Phytophaga, Sessiliventres). — Abdomen
broadly attached to the thorax (sessile). Trochanters of posterior
legs two-segmented. Ovipositor modified for boring, sawing or cutting.
Larvae with complex mouth parts, frequently caterpillar-like, with three
Pig. 29. — Papilio troilus. A, larva; B, larva suspended for pupation; C, chrysalis. Nat-
ural size.
pairs of thoracic legs and seven or eight pairs of abdominal prolegs.
Phytophagous or parasitic. Saw-flies, gall-flies, ichneumon-flies, etc.
Example, the pigeon horn-tail, Tremex (Fig. 30).
Suborder Aculeata (Heterophaga,
Petiolata.) — Abdomen petiolate or
subpetiolate (with a deep constriction
between the thoracic and abdominal
regions). First abdominal segment
(propodeum) transferred to the tho-
racic region. Trochanters of posterior
legs one-segmented. Ovipositor often
modified to form a sting. Larvae
apodous. Ants, bees, wasps, etc. Ex-
ample, the honey bee, Apis (Fig. 284).
19. Diptera. — Metamorphosis indi-
rect. Mouth parts typically sectorial,
but modified for piercing, lapping,
rasping, etc. Prothorax and meta-
thorax small, mesothorax predominant. Tarsi usually five-segmented.
One pair of wings (mesothoracic) , membranous, transparent, with
few veins; wings rudimentary or absent, however, in most of the
Pig. 30. — Tremex columba. /I, imago;
B, larva (with parasitic larva of Thalessa
attached). Natural size. — After Riley.
20 ENTOMOLOGY
parasitic species; hind wings represented by a pair of knobbed
threads, or balancers. Larvae usually eruciform, with the head fre-
quently reduced to a mere vestige with or without a pair of mandibles,
and usually without true legs, though pseudopods may be present.
Pupa naked, or enclosed in a puparium. The flies. Example, crane-
fly, Tipula (Fig. 31). About forty thousand described species.
Fig. 31. — Tipula. A, larva; B, cast pupal skin; C, imago. Slightly reduced.
20. Siphonaptera. — Metamorphosis indirect. Head small, not
sharply separated from the thorax. Eyes minute and simple, or
absent. Antennae short and
stout, situated in depressions.
Mouth parts suctorial. Body
laterally compressed. Tho-
racic segments subequal, free;
coxae large; tarsi five-segment-
ed. Wings absent or at most
quite rudimentary. Larva
with a head, mandibulate,
apodous, vermiform. Adults
saltatorial, parasitic on warm-
blooded animals. The well
(Fig. 32). One hundred and
Fig. 32. — Cat and dog flea, Ctenocephalus canis.
A, larva (after Kunckel d'Herculais); B, advdt.
Length of adult, 2 mm.
Example, Ctenocephalus
known fleas,
fifty species.
Interrelations of the Orders. — The modern classification aims to
express relationships, and these are most clearly to be ascertained by a
comparative study of the facts of anatomy and development.
The most generahzed, or primitive, insects are the Thysanura. Sub-
tracting their special, or adaptive, pecuHarities, their remaining charac-
ters may properly be regarded as inheritances from some vanished
CLASSIFICATION 2 1
ancestral type of arthropod. This primordial type, then, probably had
three simple and equal thoracic segments differing but slightly from
the ten abdominal segments; three pairs of legs and no wings; three pairs
of exposed biting mouth parts; a pair of long, many- jointed antennas
and a pair of cerci of the same description; a thin naked integument; a
simple straight alimentary canal distinctly divided into three primary
regions; a ganglion and a pair of spiracles for each of the three thoracic
and the first eight abdominal segments, if not all the latter; no meta-
morphosis; functional abdominal legs and active terrestrial habits.
The existing form that best meets these requirements is Scolopen-
drella, which is not an insect, however, but belongs in the class Sym-
phyla. The most primitive of known insects are Anajapyx and Campo-
dea, through which other insects trace their origin to the stock from
which Symphyla and Diplopoda arose.
There is not the slightest evidence to support the assumption by
Handlirsch that Thysanura and Collembola are degenerate descendants
of winged ancestors. They are primitively wingless insects (Aptery-
gota) ; in other words, they originated before insects acquired wings.
Among Thysanura, the genera Machilis and Lepisma show decided
orthopteran affinities; thus their eyes are compound and their mouth
parts strongly orthopteran; indeed, the likeness of Lepisma to a young
cockroach is striking. According to Crampton, Lepisma leads to
Plecoptera and Ephemerida; while Machilis has suggestions of affinities
with Crustacea.
"The generalized form of Thysanura, and the manner in which
it reappears in the larvae of other insects, is the natural key of the clas-
sification" (Hyatt and Arms).
Collembola, though specialized in several important ways, all
have the same peculiar kind of entognathous mouth parts as Campodea
and Japyx, for which reason and many others it is believed that Col-
lembola are an offshoot from the thysanuran stem. Collembola are
not nearly so primitive as Thysanura, however, for they have fewer
abdominal segments than the latter, exhibit much greater concentra-
tion of the nervous system, and are uniquely specialized in several
respects, notably as regards the ventral tube and the furcula, or spring-
ing organ.
Collembola are no longer regarded as a suborder of Thysanura by
those who are familiar with the morphology of the two groups. All the
specialists in Thysanura and Collembola agree in regarding them as
two distinct orders.
2 2 ENTOMOLOGY
Orthoptera probably arose directly from the original thysanuri-
form stem. Of Orthoptera, Blattidae are the most primitive, with
Mantidae closely allied to them. In a linear arrangement, Gryllidae
may follow, though not closely related to Mantidae. Between Gryl-
lidae and Tettigoniidae (formerly Locustidae) comes Walker's new family
Grylloblattidae, which a few authors prefer to regard as a new order.
Tettigoniidas and Locustidae (formerly Acridiidae) belong together.
Phasmidae have some affinities with Locustidae, but show the greatest
departure from the primitive orthopteran type.
Dermaptera, represented almost entirely by the family Forficulidae,
which some authorities still retain in the order Orthoptera, must have
come from the same ancestors as Orthoptera, needless to say. In
some respects they are more primitive than Orthoptera; in others, more
specialized. Though the order shows some thysanuran characters,
the resemblance between a young earwig and the thysanuran Japyx
(both having forceps, for example) is on the whole superficial; the mouth
parts of the two agreeing only in the broadest way. On the other hand,
the resemblances in structure between Dermaptera and Coleoptera
are deep-seated. The dermapteran genus Hemimerus has strong
affinities with the orthopteran family Blattidae.
The suborders of Platyptera are by some raised to the rank of
orders. They are so closely related, however, that it seems preferable
to the writer to express their resemblances by keeping them together,
rather than to emphasize their differences by separating them.
Platyptera, as a whole, are most nearly related to Orthoptera on the
one hand and to Plecoptera on the other; Isoptera and Embioptera in
particular being strongly orthopteran. Mallophaga, aside from their
parasitic characters, agree closely with Corrodentia, especially as
regards the structure of the head and mouth parts. The bird lice are
essentially degenerate descendants of psocid-hke ancestors (Snodgrass).
Zoraptera, represented by six species of the genus Zorotypus, is
held to be a distinct order by some authors. A few years ago, Zoro-
typus would have been placed without hesitation among the termites.
The species of the genus are essentially termites, with a wing venation
suggesting that of psocids.
Plecoptera, which Packard placed in his order Platyptera, show
many primitive characters, including thysanuriform nymphs.
The more generalized winged insects fall naturally into two
groups, which are not sharply separated, however: orthopteroid and
plecopteroid. The latter group consists of the aquatic orders Plecop-
CLASSIFICATION 23
tera, Ephemerida and Odonata. Of these, Plecoptera is probably the
most generalized order; though Ephemerida has retained some very-
primitive structures, notably the paired genital openings and ducts.
It is often stated that Plecoptera are the most primitive of winged
insec.ts. According to this view, then, Orthoptera have arisen from
the plecopteran stem. They show, however, no evidence of an aquatic
ancestry; and everything indicates that terrestrial insects preceded
aquatic. Doubtless plecopteroid and orthopteroid insects both arose
from a type that was winged, with many wing veins, mandibulate, and
terrestrial — a form like a thysanuran but with wings.
On the basis of metamorphosis, Plecoptera, Ephemerida and Odo-
nata form a natural group, Hemimetabola, in which the changes in
form during development are greater than in other Heterometabola,
the aquatic nymphs of these three orders being termed naiads by
Comstock.
Odonata are naturally placed next to Ephemerida but are strongly
aberrant forms with a unique kind of specialization.
Thysanoptera form a distinct order which is usually placed next to
Hemiptera, chiefly on account of the suctorial mouth parts, though
even in this respect there is no close agreement between the two orders.
They are aberrant and hard to place. Borner and Crampton find
resemblances between Thysanoptera and Corrodentia.
Hemiptera form a homogeneous and monophyletic order, charac-
terized by the unique shape and arrangement of the mouth parts,
which are always of the same type (Muir). Hemiptera are somewhat
like Orthoptera and possibly originated with Thysanoptera from some
mandibulate and winged form. The conversion of mandibulate into
suctorial organs may be seen within the order Collembola, though it is
improbable that Hemiptera arose from forms like Collembola. Hemip-
tera are exceptional among insects with a direct metamorphosis in
their highly developed type of suctorial mouth parts. Homoptera
are on the whole more primitive than Heteroptera.
Parasita, long a suborder of Hemiptera, should rank as an order,
apparently; though opinions differ in regard to this.
In the early days of the classification, the sucking lice and the biting
lice were always grouped together, on account of their resemblances.
Then it was found that these similarities, correlated with parasitic
existence, were only superficial; and the two groups were separated.
Some recent authors have, however, followed one another in the opinion
that the two kinds of lice are closely related to each other — an opinion
24 ENTOMOLOGY
that is surprising in view of the many strong differences of structure
between the two groups, particularly as regards the mouth parts.
Though investigators have not agreed as to the morphology of the
mouth parts of the sucking lice, a study of cross sections of the mouth
parts leads to the conclusion that they conform fundamentally to the
hemipteran type.
Metamorphosis offers the broadest criteria for the separation of
insects into primary groups. All the orders considered thus far are
characterized either by no metamorphosis or by a relatively slight, or
so-called direct, or incomplete, transformation. The following orders,
on the contrary, are distinguished by an indirect, or complete, metamor-
phosis, which appears in Coleoptera and attains its maximum develop-
ment in Hymenoptera and Diptera.
With Coleoptera the cruciform type of larva appears, as a derivative
of the earlier thysanuriform type. The larvae of Meloe, Epicauta (Fig.
220) and other genera pass from a thysanuriform stage to an cruciform
condition during their development.
It was formerly thought that the resemblances between Coleoptera
and Dermaptera were superficial, but at present there is reason to
believe that these two orders are related. They agree rather closely
in structure, especially as regards the structure of the head (Crampton)
and the thoracic sclerites (Snodgrass). Coleoptera have affinities
with Neuroptera also, that appear in some of the larvae as well as in the
adult forms. Coleoptera are, however, more primitive than Neurop-
tera, and are placed here at the beginning of the holometabolous series.
Strepsiptera should be separated from Coleoptera as a distinct
order, accepting the opinion of Dr. W. D. Pierce, who has studied the
group thoroughly. Strepsiptera are aberrant, peculiarly specialized
forms. The fact that the male strepsipteran pupa has the form of a
hymenopterous pupa may or may not be significant.
In Neuroptera, as in Coleoptera, the transition from the thysanu-
riform to the cruciform type of larva may take place during the develop-
ment of the individual, as in the larva of Mantispa.
Neuroptera have kinship with Coleoptera; the structure of the head,
for one thing, being essentially the same in the two groups. They
resemble Plecoptera also; thus a form like Sialis may have come from
ancestors like perlids.
All the orders that follow are derived from the neuropteran stem,
in the opinion of many authorities.
Mecoptera form an isolated order, though their caterpillar-like
CLASSIFICATION
25
larvae, with eleven or twelve pairs of legs, suggest affinities with Lepidop-
tera and, more remotely, with the tenthredinid Hymenoptera. Mecop-
tera are most nearly related to Neuroptera (through the genus Nemop-
tera) and have also certain affinities with Diptera (Cramp ton).
Trichoptera, while much like Mecoptera in structure and meta-
morphosis, are jindoubtedly closely related to Lepidoptera; in view of
the extensive and deep-seated resemblances between caddis flies and
the most generalized moths (Micropterygidaj) it must be concluded that
Trichoptera and Lepidoptera originated from the same stock, which
was doubtless neuropteroid.
%*»>
# .^^
DIPTERA
PLECOPTERA
PLATYPTERA
ORTHOPTERA
HEMIPTERA
THYSANURA
CQLEOPTERA
Fig. 33. — Genealogical diagram of the orders of insects.
Hymenoptera also trace their ancestry back to neuropteroid forms.
The most generalized hymenopterous larvae, those of saw-flies, are
caterpillar-like; but the most specialized larvae, as those of ants, bees,
wasps, and parasitic Hymenoptera, are more like maggots, in correlation
with their sedentary mode of life.
Hymenoptera are often called the "highest" insects, chiefly on
account of their highly developed instincts and social life. From this
point of view, however, the termites also would rank high, though
structurally they belong among the more generalized insects. As a
matter of fact, the system of classification is based necessarily on
structure, and not on psychology; and structurally Hymenoptera are,
taking everything into consideration, less specialized than Diptera.
In Diptera the eruciform type of larva attains its extreme degree of
26 ENTOMOLOGY
specialization, as in the family Muscidae. Such larvae as those of
mosquitoes are comparatively primitive.
The relationships of Diptera to other orders are not evident, but
the order is in some respects like Mecoptera. Diptera possibly came
from forms like Mecoptera, or both orders may have arisen from neu-
ropteroid ancestors.
The fleas, Siphonaptera, are usually placed next to Diptera, being
regarded as degenerate flies.
The preceding diagram (Fig. 33) is a graphic summary of the gen-
ealogy of some of the orders of insects. The central group (T) is the
hypothetical thysanuroid source of all insects, including Thysanura
themselves. Though Thysanura and Collembola show no traces of
wings, even in the embryo, it should be borne in mind that all the other
insects probably had winged ancestors and that it is more reasonable to
assume a single winged group as a starting point than to suppose that
wings originated independently in several different groups of insects.
CHAPTER II
ANATOMY AND PHYSIOLOGY
I. Skeleton
Number and Size of Insects. — The number of insect species al-
ready known is about 400,000 and it is safe to estimate the total number
of existing species as at least one million.
Among the largest living species are the Venezuelan beetle, Dynastes
hercules, which is 155 mm. long, and the Venezuelan grasshopper,
Tropidacris latreillei, which has a length of 166 mm. and an alar expanse
of 240 mm. Among Lepidoptera, Attacus atlas of Indo-China spreads
240 mm.; Attacus casar oi the Philippines, 255 mm.; and the Brazilian
noctuid Erebus agrippina, 280 mm. Some of the exotic wood-boring
larvae attain a length of 150 mm.
The giants among insects have been found in the Carboniferous,
from which Brongniart described a phasmid (Titanophasma) as being
one-fourth of a meter long, and a huge dragon fly {Meganeura) with
a spread of more than two feet.
At the other extreme are beetles of the family Trichopterygidae,
some of which are only 0.25 mm. in length, as are also certain hymenop-
terous egg-parasites of the families Chalcididse and Proctotrypidae.
Thus, as regards size, insects occupy an intermediate place among
animals; though some insects are smaller than the largest protozoans
and others are larger than the smallest vertebrates.
Segmentation. — One of the fundamental characteristics of arthro-
pods is their linear segmentation. The subject of the origin of this seg-
mentation is far from simple, as it involves some of the most difficult
questions of heredity and variation. As arthropod segmentation is
usually regarded as an inheritance from annelid-like ancestors, the sub-
ject resolves itself into the question of the origin of the segmented
from the unsegmented "worms." Cope, Packard and others give the
mechanical explanation which is here summarized. In a thin-skinned,
unsegmented worm, the flexures of the body initiated by the muscular
system would throw the integument into folds, much as in the leech,
and with the thickening of the integument, segmentation would appear
from the fact that the deposit of chitin would be least at the places of
27
28 ENTOMOLOGY
greatest flexure, i. e., the valleys of the folds, and greatest at the places
of least flexure, i. e., the crests of the folds. This explanation, which
has been elaborated in some detail by the Neo-Lamarckians, applies
also to the segmentation of the limbs, as well as the body.
Head. — In an insect several of the most anterior pairs of primary
appendages have been brought together to co-operate as mouth parts
and sense organs, and the segments to which they belong have become
compacted into a single mass — the head^- in which the original seg-
mentation is difficult to trace. The thickened cuticula of the head forms
a skull, which serves as a fulcrum for the mouth parts, furnishes a base
of attachment for muscles and protects the brain and other organs.
While the jaws of most insects can only open and shut, transversely,
their range of action is enlarged by movements of the entire head, which
are permitted by the articulation between the head and thorax.
As a rule, one segment overlaps the one next behind; but the head,
though not a single segment of course, never overlaps the prothorax in
the typical manner, but is usually received into that segment. This
condition, which may possibly have been brought about simply by the
backward pull of the muscles that move the head, has certain
mechanical advantages over the alternative condition, in securing,
most economically, freedom of movement of the head and protection
for the articulation itself.
The size and strength of the skull are usually proportionate to the
size and power of the mouth parts. In some insects almost the entire
surface of the head is occupied by the eyes, as in Odonata (Fig. 21, B)
and Diptera (Fig. 40). In muscid and many other dipterous larvae, or
"maggots," the head is reduced to the merest rudiment.
Though commonly more or less globose or ovate, the head presents
innumerable forms; it often bears unarticulated outgrowths of various
kinds, some of which are plainly adaptive, while others are apparently
purposeless and often fantastic.
Sclerites and Regions of the Skull. — The dorsal part of the skull
(Fig. 34) consists almost entirely of the epicranium, which bears the
compound eyes; it is usually a single piece, or sclerite, though in some
of the simpler insects it is divided by a Y-shaped suture, the epicranial
suture. The middle of the face, where the median ocellus often occurs,
is termed the front; ordinarily this is simply a region, though a frontal
sclerite exists in some insects between the branches of the epicranial
suture. Just above the front, and forming the summit of the head, is
the region known as the vertex; it often bears ocelli. The clypeus is
ANATOMY AND PHYSIOLOGY
29
easily recognized as being the sclerite to which the upper Hp, or lahrum,
is hinged, though the clypeus is not invariably delimited as a distinct
sclerite. In certain insects a transverse suture divides the clypeus
into an anteclypeus and a postdypeus. The cheeks of an insect are
known as the gencB, and post-gence sometimes occur. On the under side
of the head is the gula, which bears the under lip, or labium. That part
of the skull nearest the pro thorax is termed the occiput; usually it is not
delimited from the epicranium, though in some insects it is continuous
with the post-genai to form a distinct sclerite. The occiput surrounds
the opening known as the occipital foramen, through which the oesopha-
FiG. 34. — Skull of a grasshopper, Melanoplus differenlialis. a, antenna; c, clypeus; e,
compound eye; /, front; g, gena; I, labrum; i^, labial palpus; m, mandible; mp, maxillary
palpus; o, ocelli; oc, occiput; pg, post-gena; v, vertex.
gus and other organs pass into the thorax. The membrane of the
neck in Orthoptera and some other insects contains small cervical
sclerites, dorsal, lateral or ventral in position; these, in the opinion of
Comstock, pertain to the last segment of the head. Besides those
described, a few other cephalic sclerites may occur, small and incon-
spicuous, but nevertheless of morphological importance; for example,
ocular or antennal sclerites, bearing the eyes or the antennas, respec-
tively; and the trochantin of the mandible, situated between the mandi-
ble and gena.
Tentorium. — In the head is a chitinous supporting structure known
as the tentorium. This consists of a central plate from which diverge
either two or three pairs of arms {anterior, posterior and dorsal) extending
so
ENTOMOLOGY
to the skull (Fig. 35). The central plate, or body, lies between the
brain and the suboesophageal ganghon and under the oesophagus, which
passes between the anterior pair of arms. The tentorium braces the
skull, affords muscular attachments and holds the cephalic ganglia and
the oesophagus in place. It is not a true internal skeleton, but arises
Fig. 35. — Skull of a grasshopper, Dissos
teira Carolina, o, occipital foramen; t, t,
anterior arms of tentorium.
Fig. 36.
-Head of a gyrinid beetle, Dineutus,
to show divided eye.
from the same ectodermal layer which produces the external cuticula;
though authors are not agreed as to the details of the development.
Eyes. — The eyes are of two kinds — simple and compound. The
latter, or eyes proper, conspicuous on each side of the head, are of com-
FiG. 37. — Agglomerate eyes of a male coccid,
Leachia fuscipennis. — After Signoret.
Fig. 38. — FacuU '^^i a compound eye of
Melanoplus. Highly magnified.
mon occurrence except in the larvae of most holometabolous insects, in
some generalized forms (as Collembola) and in parasitic insects. The
compound eyes (Fig. 41) are convex and often hemispherical, though
their outline varies greatly; thus it may be oval (Orthoptera) or triangu-
lar (Notonecta), while in the aquatic beetles of the family Gyrinidae
(Fig. 36) each eye has a dorsal and a ventral lobe, enabhng the insect
to see upward and downward at the same time ; so also in Oberea and
ANATOMY AND PHYSIOLOGY
31
other terrestrial beetles of the same family. Superficially, a compound
eye is divided into minute areas, or facets, which though circular in the
agglomerate type of eye (Fig. 37) are commonly more or less hexagonal
(Fig. 38), as the result of mutual pressure. These facets are not
necessarily equal in size, for in dragon flies the dorsal facets are fre-
quently larger than the ventral. In diame-
ter the facets range from .016 mm. {Lycana)
to .094 mm. {Ceramhyx). Their number is
often enormous; thus the house fly {Musca
domestica) has 4,000 to each eye, a butterfly
{Papilio) 17,000, a beetle (Mordella) 25,000
and a sphingidmoth 27,000; on the other hand,
ants have from 400 down, the worker ant of
Eciton having at most a single facet on each
side of the head.
Ocelli. — The simple eyes, or ocelli, appear
as small polished lenses, either lateral or dor-
sal in position. Lateral ocelli (Fig. 39) occur
Fig.
39-
^^ -Head of a cater-
in the larvae of most holometaboloUS insects pillar Samia cecropia, to show
and in parasitic forms. Dorsal ocelli, sup- ^^'''^^ °'^""^-
plementary to the compound eyes, occur on or near the vertex, and
are more commonly three in number, arranged in a triangle, as in
Odonata, Diptera (Fig. 40) and Hymenoptera (Fig. 41) as well as many
Orthoptera and Hemiptera. Few beetles have ocelli and almost no
^ A
^-r-^^y-
Fig. 40.^ — Ocelli and compound eyes of a fly, Phormia regina. A, male; B, female.
butterflies (Lerema accius with its one ocellus being the only exception
known), though not a few moths have two ocelli.
As explained beyond, the compound eyes are adapted to perceive
form and movements and the ocelli to form images of objects at close
range or simply to distinguish between Hght and darkness.
Sexual Differences in Eyes. — In most Diptera (Fig. 40) and in
Hymenoptera (Fig. 41) and Ephemeridas as well, the eyes of the male are
32
ENTOMOLOGY
larger and closer together (holoptic) than those of the female (dichoptic).
This difference is attributed to the fact that the male is more active
Fig. 41.— Ocelli and compound eyes of the honey bee. Apis mellifera. A. queen; B,
drone. — After Cheshire.
Fig. 42. — Various forms of antennae. A, fiUform, Eiischistus; B, setaceous, Plathemis;
C, moniliform, Catogenus; D, geniculate, Bombus; f, flagellum; ^.pedicel; 5, scape; E, irreg-
ular, Phormia; a, arista; F, setaceous, Galerita; G, clavate, Anosia; H, pectinate, male
Ptilodaclyla; I, lamellate, Lachnosterna; J, capitate, Megalodacne; K, irregular, DinetUus.
than the female, especially in the matter of seeking out the opposite sex.
ANATOMY AND PHYSIOLOGY 33
Among ants of the same species the different forms may differ greatly
in the number of lateral facets. Thus in Formica pratensis, according to
Forel, the worker has about 600 facets in each eye, the queen 800-900
and the male 1,200.
Blind Insects. — Many larva?, surrounded by an abundance of food
and living often in darkness, need no eyes and have none; this is true of
the dipterous "maggots" and many other sedentary larvas, particularly
such as are internal parasites (Tachinidge, Ichneumonidae), or such as
feed within the tissues of plants (many Buprestidae, Cerambycidae and
CurcuHonidcE). Subterranean or cavernicolous insects are either
eyeless or else their eyes are more or less degenerate, according to the
amount of light to which they have
access. The statement is made that
blind insects never have functional
wings.
Antennae. — The antennae, never
more than a single pair (though
embryonic "second antennae " occur
in Thysanura and Collembola), are
situated near the compound eyes and
frequently between them. With rare
exceptions the antennae have always
several and usually many segments.
In form these organs are exceedingly
varied, though many of them may
be referred to the types represented Fi^. 43.— Antennje of a moth. Samia
cecropia. A, male; B, female.
in Figs. 42-44.
Though homologous in all insects, the antennae are by no means equiv-
alent in function. They are commonly tactile (grasshoppers, etc.) or
olfactory (beetles, moths) and occasionally auditory (mosquito), as
described beyond, but may be adapted for other than sensory functions.
Thus the antennae of the aquatic beetle Hydrophilus are used in connec-
tion with respiration and those of the male Meloe to hold the female.
Sexual Differences in Antennae. — In moths of the family Saturniidee
[S. cecropia, C. promethea, etc.) the pectinate antennae of the male are
larger and more feathered than those of the female, and differ also in
having more segments (Fig. 43). Here the antennae are chiefly olfac-
tory, and the reason for their greater development in the male appears
from the fact that the male seeks out the female by means of the sense
of smell and depends upon his antennae to perceive the odor emanating
from the opposite sex.
34
ENTOMOLOGY
The plumose antennae of the male mosquito (Fig. 44) are highly de-
veloped organs of hearing, and are used to locate the female ; they have
delicate fibrillae of various lengths, some of which are thrown into sym-
pathetic vibration by the note of the female (p. 94).
Meloe has just been mentioned. In Sminthurus malmgrenii (Collem-
bola) the antennae of the male are provided with hooks and otherwise
adapted to grasp those of the female at copulation.
Though systematists have recorded many instances of antennal
antigeny, the interpretation of these sexual differences has received very
little attention; a beginning in the subject has been made by Schenk,
whose results will be referred to in connection with the sense organs.
Fig. 44. — Antennae of mosquito, Culex pipiens. A, male; B, female. The antenna has a
short basal segment, not shown in the figure.
Mouth Parts. — On account of their great range of differentiation,
the mouth parts are of fundamental importance to the systematist, par-
ticularly for the separation of insects into orders. Most of the orders
fall into two groups according as the mouth parts are either biting
(mandibulate) or sucking {suctorial). Collembola and Hymenoptera,
however, combine both functions; Diptera, though suctorial, exhibit
various modifications for piercing, lapping or rasping; Thysanoptera
are partly mandibulate but chiefly suctorial; and adult Ephemerida
and Trichoptera have but rudimentary mouth parts.
The mandibulate orders are Thysanura, Collembola (primarily),
Orthoptera, Dermaptera, Isoptera, Embioptera, Corrodentia, Mal-
lophaga, Plecoptera, Ephemerida (rudimentarily in adult), Odonata,
Coleoptera, Strepsiptera, Neuroptera and Mecoptera.
ANATOMY AND PHYSIOLOGY
35
The usual statement is that there are three pairs of mouth parts,
namely, mandibles, maxillcB and labium. As a matter of fact, there are
four pairs, counting the superlingucB, which are evident in Thysanura
and Collembola, become vestigial in Heterometabola, and disappear in
the most specialized Holometabola. The mandibulate, or primary
type (Fig. 45), from which the suctorial, or secondary type, has been
derived, will be considered first.
Mandibulate Type. — The labrum, or upper lip, in biting insects is a
simple plate, hinged to the clypeus and moving up and down; though
capable of protrusion and retraction to some extent. It covers the man-
FiG. 45. — Mouth parts of a cockroach, Parcoblatta pennsylvanica. A, labrum; B,
mandible; C, hypopharynx; D, maxilla; E, labium; c, cardo; g (of maxilla), galea; g (of
labium), glossa; /, lacinia; /^, labial palpus; m, mentum; mp, maxillary palpus; p, paraglossa;
pf, palpifer; pg, palpiger; s, stipes; sm, submentum. B, D, and E are in ventral aspect.
dibles in front and pulls food back to these organs. On the roof of the
pharynx, under the labrum and clypeus, is the epipharynx; this consists
of teeth, tubercles or bristles, which serve in some insects merely to hold
food, though as a rule the epipharynx in mandibulate insects bears end-
organs of taste (Packard). The labrum does not represent a pair of
primary appendages.
The mandibles, or jaws proper, move in a transverse plane, being
closed by a pair of strong adductor muscles and opened by a pair of
weaker abductors. The mandible is almost always a single solid piece.
In herbivorous insects (Fig. 46, A) it is compact, bluntly toothed, and
36
ENTOMOLOGY
often bears a molar, or crushing, surface behind the incisive teeth. In
carnivorous species (B) the mandible is usually long, slender and sharply
toothed, without a molar surface. Often, as in soldier ants, the man-
dibles are used as piercing weapons; in bees (C) they are used for various
industrial purposes; in some beetles they are large, grotesque in form and
apparently purposeless. The mandibles of Onthophagus (D) and many
other dung beetles consist chiefly of a flexible lamella, admirably adapted
for its special purpose. In Euphoria (Fig. 265), which feeds on pollen
and the juices of fruits, the mandibles, and the other mouth parts as
well, are densely clothed with hairs. In the larva of Chrysopa, the
inner face of the mandible (Fig. 46, E) has a longitudinal groove against
which the maxilla fits to form a canal, through which the blood of
Pig. 46. — Various forms of mandibles. A, Melanoplus; B, Cicindela; C, Apis; D, Onthoph-
agus; E, Chrysopa; F-I, soldier termites (after Hagen).
plant lice is sucked into the oesophagus. In termites (F-I) the mandi-
bles assume curious and often inexplicable forms.
Next in order are the superlingua {maxillulcB) , which have been
overlooked or disregarded by most entomologists. The superlinguas
are well developed in Thysanura and Collembola, particularly the
former order. In Machilis, for example, the superlingua has essentially
the same structure as a maxilla, as appears in Fig. 47; in Japyx the
palpus is three-segmented (Hansen). The superlinguae, arising in the
embryo as a separate pair of appendages (Fig. 198, si), always become
united by their bases with the lingua (Fig. 198, In), forming a pair of
wing-like appendages on the dorsal side of the lingua (Figs. 50, 51).
Among insects, superlinguae are best developed in Thysanura and
Collembola, and are known to occur also in Orthoptera, Dermaptera,
Isoptera, Corrodentia, nymphs of Ephemerida and larvae of some
Coleoptera.
Hansen ('93) termed these appendages "maxillulae," regarding
them as homologous with the first maxillae of Crustacea; and in this
ANATOMY AND PHYSIOLOGY
37
interpretation he was followed by others, including the writer, who
(Folsom, 'go) termed them "superlinguai." The writer at present
agrees with Crampton, however, that these appendages are homologous
with the paragnaths of Crustacea. If they are not equivalent to the
first maxillae of Crustacea, the term "maxillulae" should not be applied
to them; they may be termed " superlinguse " or "paragnaths," as one
prefers.
Following the superlinguae are the maxillcB, or under jaws, which are
less powerful than the mandibles and more complex, consisting as they
do of several sclerites (Figs. 45, 48). Essen-
tially, the maxilla consists of three lobes,
namely, palpus, galea and lacinia, which are
borne by a stipes, and hinged to the skull by
means of a cardo. The palpus, always lateral
in position, is usually four- or five-segmented
and is tactile, olfactory or gustatory in function.
The lacinia is commonly provided with teeth or
spines. The maxillae supplement the mandi-
bles by holding the food when the latter open,
and help to comminute the food. Additional
maxillary sclerites, of minor importance, often
occur.
The labium, or under lip, may properly be
likened to a united pair of maxillae, for both
are formed on the same three-lobed plan.
This correspondence is evident in the cock-
roach, among other generalized insects. Thus, in this insect (Fig. 45) :
Labium = Maxilla
palpus = palpus
paraglossa = galea
glossa = lacinia
palpiger = palpifer
menium = stipites
suhmentum with gula = cardines
In most mandibulate orders the glossae unite to form a single me-
dian organ, as in Harpalus (Fig. 49, g). The labium forms the floor of
the pharynx and assists in carrying food to the mandibles and maxillae.
The tongue, or hypopharynx, is a median fleshy organ (Fig. 45)
which is usually united more or less with the base of the labium. In
Fig. 47. — Left superlingua
of Machilis variabilis. g,
galea; /, lacinia; p, palpus.
38
ENTOMOLOGY
insects in general, the salivary glands open at the base of the hypo-
pharynx. In the most generalized insects, Thysanura and Collembola.
the hypopharynx is a compound organ, consisting of a median ventral
lobe, or lingua, and two dorsolateral lobes, termed superlingucs by the
Fig. 48. — Maxilla of Har pains caliginosus,
ventral aspect, c, cardo; g, galea; /, lacinia;
p, palpus; pf, palpifer; s, stipes; sg, subgalea.
Pig. 49. — Labium of Harpalus caliginosus,
ventral aspect, g, united glossae, termed
the glossa; m, mentum; p. palpus; pg, palpi-
ger; pr, paraglossa; sm, submentum. The
median portion of the labium beyond the
mentum (excepting the palpi) is termed the
ligula.
author. Superlinguse occur in other mandibulate orders just mentioned,
but have not yet been recognized in the most specialized orders of
insects.
Fig. 50. — Hypopharynx of Hemitnerus
talpoides. I, lingua; s, superlingua. — After
Hansen.
Fig. s i .• — Hypopharynx of an ephemerid,
Heptagenia. I, lingua; si, si, superlingua5. —
After Vayssiere.
Suctorial Types. — The mandibulate type of mouth parts is the
primitive type, from which the suctorial types have been derived.
Though the latter have evolved in several directions, they may all
be homologized with the former.
ANATOMY AND PHYSIOLOGY
39
The suctorial, or haustellate, orders, are CoUembola (in part),
-Thysanoptera (in part), Hemiptera, Parasita, Trichoptera (imper-
fectly), Lepidoptera, Diptera, Siphonaptera and Hymenoptera (which
have functional mandibles, however).
Hemiptera. — The beak, or rostrum, in Hemiptera consists (Fig. 52)
of a conspicuous, one- to four-segmented labium, which ensheathes hair-
like mandibles and maxillae and is covered above at its base by a short
Fig. 52. — Mouth parts of a hemipteron, Benacus grisens. A, dorsal aspect; B, trans-
verse section; C, extremity of mandible; D, transverse section of mandibles and maxillae
c, suction canal; I, labrum; li, labium; m, mandible; mx, maxillae.
labrum. The mandibles and maxillae are sharply-pointed, piercing
organs and the former frequently bear retrorse barbs just behind the
tip ; the two maxillae lock together to form a sucking tube with two
canals: an upper, suction canal and a lower, salivary canal. Though
primarily a sheath, the labium bears at its extremity sensory hairs,
which are doubtless used to test the food. This general description
appUes to all Hemiptera except the parasitic forms, which present
special modifications. A pharyngeal pumping apparatus is present,
which is similar in its general plan to that of Lepidoptera and Diptera,
40
ENTOMOLOGY
as presently described, though it differs as regards the smaller details of
construction.
Lepidoptera.— In Lepidoptera, excepting Eriocephala, the labrum is
reduced (Fig. 53) and the mandibles are either rudimentary or absent
(Rhopolscera). The two maxillae are represented by their galeae,
which form a conspicuous proboscis; the grooved inner faces of the galeae
(or laciniae, according to Kellogg) form the sucking tube, which opens
into the oesophagus. The labium is reduced, though the labial palpi
(Fig. 54) are well developed. The so-
called rudimentary mandibles of Anosia
and other forms have been shown by
Kellogg to be lateral projections of the la-
brum (Fig. 53) and are ^rvovfn 2i^ pilifers .
Fig. 53. — Head of a sphingid moth, Pro-
toparce sexla. a, antenna; c, clypeus; e, eye;
I, labrum; m, mandible; ^, pilifer; />r, proboscis.
Fig. 54. — Head of a butter-
fly, Vanessa, a, antennae; I,
labial palpus; p, proboscis.
The exceptional structure of the mouth parts in the generalized
genus Eriocephala (Micropteryx) sheds much light on the morphology
of these organs in other Lepidoptera, as Walter and Kellogg have shown.
In this genus there are functional mandibles; the maxilla presents
palpus, galea, lacinia, stipes and cardo, though there is no proboscis;
the labium has well developed submentum, mentum and palpi; a
hypopharynx is present.
The sucking apparatus, as described by Burgess, is essentially like
that of Diptera. Five muscles, originating at the skull and inserted
on the wall of a pharyngeal bulb, serve to dilate the bulb that it may
suck in fluids, while numerous circular muscles serve by contracting
successively to squeeze the contents of the bulb back into the stomach ;
a hypopharyngeal valve prevents their return forward.
ANATOMY AND PHYSIOLOGY
41
Diptera. — In the female mosquito the mouth parts (Fig. 55) are
long and slender. As Dimmock found, the labrum and epipharynx
combine^ to form a sucking tube; the mandibles and maxillai are delicate,
linear, piercing organs, the latter being barbed distally; maxillary
palpi are present ; the hypopharynx is linear also and serves to conduct
saliva; the labium forms a sheath, enclosing the other mouth parts
when they are not in use; a pair of sensory lobes, termed labella, occur
at the extremity of the labium.
Fig. 55. — Mouth parts of female mosquito, Culex pipiens. A, dorsal aspect; B, trans-
verse section; C, extremity of maxilla; D, extremity of labrum-epipharynx; a, antenna; e,
compound eye; h, hypopharynx; /, labrum-epipharynx; li, labium; tn, mandible; mx,
maxilla; p, maxillary palpus. — B, after Dimmock.
The oesophagus is dilated to form a bulb, or sucking organ, from
which muscles pass outward to the skull; when these contract, the
bulb dilates and can suck in fluids, as blood or water, which are forced
back into the stomach by the elasticity of the bulb itself, according to
Dimmock; the regurgitation of the food is prevented by a valve.
The male mosquito rarely if ever sucks blood, and its mouth parts
differ from those of the female in having the mandibles aborted and the
maxillae slightly developed, but with long palpi, while the hypopharynx
coalesces with the labium and there is no oesophageal bulb.
1 Kulagin, however, described them as remaining separate.
42
ENTOMOLOGY
Hymenoptera. — In the honey bee, which will serve as a type, the
labrum is simple; the mandibles are well developed instruments for
cutting and other purposes (Fig. 56) and the remaining mouth parts
form a highly complex suctorial apparatus, as follows. The "tongue''
(glossa) is a long flexible organ, terminating in a "spoon" {labellum,
Figs. 56, 129) and clothed with hairs of various kinds, for gathering
Fig. 56. — Mouth parts of the honey bee, Apis mellifera, ventral aspect, c, cardo; g,
ssa (united glossae); I, lorum; lb, labellum; Ip, labial palpus; m, mentum; md, mandible;
mp. maxillary palpus; mx, maxilla; p, paraglossa; pg, palpiger; s, stipes (plus subgalea and
palpifer) ; sm, submentum. The blade of the maxilla is the galea, and the rounded lobe
opposite the palpus is the lacinia.
nectar or for sensory or mechanical purposes. The maxillae and labial
palpi form a tube embracing the tongue, while the epipharynx fits into
the space between the bases of the maxillae to complete this tube.
Through this canal nectar is driven, by the expansion and contraction
of the tube itself, according to Cheshire, except that when only a small
quantity of nectar is taken, this passes from the spoon into a fine "cen-
ANATOMY AND PHYSIOLOGY
43
tral duct," or also into the "side ducts," which are specially fitted to
convey quantities of fluid too small for the main tube. For a detailed
account of the highly complex and exquisitely adapted mouth parts of
the honey bee, the reader is referred to Cheshire's admirable work,
Packard's Text-Book, or Snodgrass' The Anatomy of the Honey Bee.
Segmentation of the Head. — The determination of the number of
segments entering into the composition of the insect head has been a
difficult problem. As no segment bears more than one pair of primary
appendages, there are at least as many segments in the head as there are
fBr.°° o^»aj3 "aSi
Fig. 57. — Paramedian section of an embryo of the coUemboIan Anurida marilima; to
show the primitive cephalic ganglia, i, ocular neuromere; 2, antennal; 3, intercalary;
4, mandibular; 5, superlingual; 6, maxillary; 7, labial; 8, prothoracic; 9, mesothoracic; a;
antenna; /, labnim; Zt, labium; U, I'', P, thoracic legs; tn, mandible; mx, maxilla.- — After
FOLSOM.
pairs of primary appendages. On this basis, then, the antennae, man-
dibles, maxillae and labium may be taken to indicate so many segments;
but in order to decide whether the eyes, labrum and hypopharynx repre-
sent segments, other than purely anatomical evidence is necessary. The
key to the subject is furnished by embryology. At an early stage of
development the future segments are marked off by transverse grooves
on the ventral surface of the embryo, and the pairs of segmental appen-
dages are all alike (Fig. 197), or equivalent, though later they differen-
tiate into antennae, mouth parts, legs, etc. Moreover, the nervous
44 ENTOMOLOGY
system exhibits a segmentation which corresponds to that of the entire
insect; in other words, each pair of primitive gangha, constituting a
neuromere, indicates a segment. Now in front of the oesophagus three
primitive segments appear, each with its neuromere (Fig. 57): first in
position, an ocular segment, destined to bear the compound eyes;
second, an antennal segment; third, an intercalary (premandibular)
segment, which in the generalized orders Thysanura and Collembola
bears a transient pair of appendages that are probably homologous with
the second antennae of Crustacea. In the adult, the ganglia of these
three segments have united to form the brain, and the original simpli-
city and distinctness have been lost. The labrum, by the way, does
not represent a pair of appendages, but arises as a single median lobe.
Behind the oesophagus, three embryonic segments are clearly distin-
guishable, each with its pair of appendages, namely, mandibular,
maxillary and labial. Finally, the hypopharynx, or rather a part of
it, claims a place in the series of segmental appendages, as the author
has maintained; for in Collembola its two dorsal constituents, or super-
lingucB, develop essentially as do the other paired appendages and, more-
over, a superlingual neuromere (Fig. 57) exists (even though Philip-
tschenko failed to find it). The four primitive ganglia immediately
behind the mouth eventually combine to form the suboesophageal
ganglion.
To summarize — the head of an insect is composed of at least six seg-
ments, namely, ocular, antennal, intercalary, mandibular, maxillary
and labial; and at most seven, since a superHngual segment occurs
between the mandibular and maxillary segments in Collembola and
Thysanura.
Thorax. — The thorax, or middle region, comprises the three segments
next behind the head, which are termed, respectively, pro-, meso- and
metathorax. In aculeate Hymenoptera, however, the thoracic mass in-
cludes also the first abdominal segment, then known as the propodeum,
or median segment. Each of the three thoracic segments bears a pair
of legs in almost all adult insects, but only the meso- and metathorax
may bear wings.
The dift"erentiation of the thorax as a distinct region is an incidental
result of the development of the organs of locomotion, particularly the
wings. Thus in legless (apodous) larvae the thoracic and abdominal
segments are alike; when legs are present, but no wings, the thoracic
segments are somewhat enlarged; and when wings occur, the size of a
wing-bearing segment depends on the volume of the wing muscles.
ANATOMY AND PHYSIOLOGY 45
which in turn is proportionate to the size of the wings. When wings
are absent (as in Thysanura and CoUembola) or the two pairs equal
in area (as in Termitidae, Odonata, Trichoptera and most Lepidoptera)
the meso- and metathorax are equal. If the fore wings exceed the
hind ones (Ephemeridae, Hymenoptera) the mesothorax is proportion-
ately larger than the metathorax; as also in Diptera, where no hind
wings occur. If the fore wings are small (Coleoptera) or almost
absent (Stylopidae) the mesothorax is correspondingly smaller than the
metathorax. The prothorax, which never bears wings, may be enlarged
dorsally to form a protective shield, as in Orthoptera, Hemiptera and
Coleoptera; or, on the contrary, may be greatly Pes/
reduced, as in Ephemerida, Odonata, Lepi-
doptera and Hymenoptera. In the primitive V— 7t-
Apterygota the prothorax may become re-
duced (many Collembola) or slightly enlarged P^''
{Lepisma) .
The dorsal wall of a thoracic segment is
termed the notum, or tergum; the ventral wall, Pig. 58.— Diagram of the
the stermmi; and each lateral wall, a pleuron; p"':^^^?^! ^^Y"'^^ °^-^ *^°'
' ' J: ' racic segment, ew.epimeron;
the restriction of these terms to particular es, epistemum; p, prsscutum;
segments of the thorax being indicated by the iCmr^'^^^Sum;?/. sSSuim-
prefixes pro-, meso- or meta-. These parts are -s^ sternum.— After Comstock.
usually divided by sutures into distinct pieces, or sclerites, as represented
diagrammatically in Fig. 58. Thus the tergum of a wing-bearing
segment is regarded as being composed of four sclerites {tergites, Fig.
59), namely and in order, prcescutum, scutum, scutellum and postscu-
tellum. The scutum and scuteUum are commonly evident, but the
two other sclerites are usually small and may be absent. According
to Snodgrass, the tergum consists primitively of a single sclerite, the
notum; the four sclerites having arisen as specializations; being not
always homologous in different orders of insects. Each pleuron con-
sists chiefly of two sclerites {pleurites, Figs. 58 and 60), separated from
each other by a more or less oblique suture. The anterior of these
two, which joins the sternum, is termed the epistemum; the other, the
epimeron. The former is divided into two sclerites in Odonata and
both are so divided in Neuroptera.
The sternum, though usually a single plate, is in some instances
divided into halves, as in the cockroach, or even into five sclerites
(Forficulidae) .
To these should be added the patagia of Lepidoptera — a pair of
46
ENTOMOLOGY
erectile appendages of the prothorax; and the tegulce (paraptera) of
Lepidoptera, Diptera and Hymenoptera — a pair of small sclerites at
the bases of the front wings.
The thorax has also several small sclerites which are not described
here, though they are of interest to the morphologist.
Each of the three thoracic segments bears a pair of spiracles in
the embryo, but in most imagines there are only two pairs of thoracic
spiracles, the suppressed pair being the prothoracic.
The sclerites of the thorax owe their origin probably to local strains
on the integument, brought about by the muscles of the thorax. Thus
the primitively wingless Thysanura and
CoUembola have no hard thoracic
sclerites, though certain creases about
the bases of the legs may be regarded
as incipient sutures, produced mechan-
ically by the movements of the legs.
In soft njrmphs and larvae, the sclerites
■0 do not form until the wings develop;
and in forms that have nearly or quite
lost their wings, as Pedicuhdae, Mallo-
phaga, Siphonaptera and some para-
sitic Diptera, the sclerites of the thorax
tend to disappear. Furthermore, the
absence of sclerites in the prothorax is
Fig. 59.— Dorsal aspect of the tho- probably duc to the lack of prothoracic
rax of a beetle, Hydrous piceus. 1,
pronotum; 2, mesopraescutum; 3, WingS
mesoscutum; 4. mesoscutellum; 5. obsolete SUturCS of the
mesopostscutellum; 6, metapraescu-
tum; 7, metascutum; 8, metascutellum; graSshoppcrs.
9, metapostscutellum. — After New-
port.
not withstanding the so-called
pronotum in
Endoskeleton. — An insect has no
internal skeleton, strictly speaking,
though the term endoskeleton is used in reference to certain ingrowths of
the external cuticula which serve as mechanical supports or as protec-
tions for some of the internal organs. The tentorium of the head has
already been referred to. In the thorax three kinds of chitinous in-
growths may be distinguished according to their positions: (i) phrag-
mas, or dorsal projections; (2) apodemes, lateral; (3) furcce, or apo-
physes, ventral. The phragmas (Fig. 61) are commonly three large
plates, pertaining to the meso- and metathorax, and serving for the
origin of indirect muscles of flight in Lepidoptera, Diptera, Hymenop-
tera and other strong-winged orders. The apodemes are comparatively
ANATOMY AND PHYSIOLOGY
47
small ingrowths, occurring sometimes in all three thoracic segments,
though usually absent in the prothorax. The furcae occur in each
thoracic segment as a pair of conspicuous processes, which either
remain separate or else unite more or less; leaving, however, a passage
for the ventral nerve cord.
-
' w
m::.L
/ ^ J
t
a
a
:
Fig. 6o. — Ventral aspect of a carabid beetle, Galerita janus. i, prosternum ; 2, proepi-
sternum; 3, proepimeron; 4. coxal cavity; 5. inflexed side of pronotum; 6. mesosternum; 7.
mesoepis'ternum; 8, mesoepimeron ; 9. metasternum; 10, antecoxal piece; 11, metaepi-
sternum- 12, metaepimeron; 13. inflexed side of elytron; a. sternum of an abdominal seg-
ment; an. antenna; c, coxa; /, femur; Ip, labial palpus; md. mandible; mp, maxillary pal-
pus; /, trochanter; tb, tibia; ts, tarsus.
These endoskeletal processes serve chiefly for the origin of muscles
concerned with the wings or legs, and are absent in such wingless forms
as Thysanura, Pediculidae and Mallophaga.
Some ambiguity attends the use of these terms. Thus some writers
48
ENTOMOLOGY
use the term apodemes for furcse and others apply the term apodeme
to any of the three kinds of ingrowths.
Legs. — In almost all adult insects and in most larvae each of the
three thoracic segments bears a pair of legs. The leg is articulated to
the sternum, episternum and epimeron, partly by means of small
articular sclerites (one of which, the trochantin, is shown in Fig. 63)
and consists of five segments (Fig. 62), in the
following order: coxa, trochanter, femur, tibia,
tarsus. The coxa is the basal segment. The
trochanter is small and in parasitic Hymenop-
tera consists of two subsegments. The femur
is usually stout and conspicuous, the tibia
commonly slender. The tarsus, rarely single-
jointed, consists usually of five segments, the
last of which bears a pair of claws in the adults
of most orders of insects and a single claw in
larvae; between the claws in most imagines is a
pad, usually termed the pulvillus, or empodium.
Adaptations of Legs. — The legs exhibit a
great variety of adaptive modifications. A
walking ' or running insect, as a carabid or
cicindelid beetle (Fig. 64, A) presents an aver-
FiG. 61. -Transverse sec- ^ge Condition as regards the legs. In leaping
tions of the thoracic segments insccts (grasshoppers, crickcts, Haltica) the
of a beetle, Co/Ja</z!i5, to show , . , . ^ ^ / ■n\
the endoskeietai processes, hmd fcmora are enlarged {B) to accommodate
A, prothorax; 5. mesotho- ^j^^ powerful cxtcusor musclcs. In insccts that
rax; C, metathorax; a, a, ^
furcae; ad, apodeme; p, make little use of their legs, as May flies and
p ragma. ter olbe. xipulidse, these appendages are but weakly
developed. The spinous legs of dragon flies form a basket for catching
the prey on the wing. Modifications of the front legs for the
purpose of grasping occur in many insects, as the terrestrial
families Mantidae (C) and Reduviidae and the aquatic famihes
Belostomidae and Naucoridae (D). Swimming species present special
adaptations of the legs (Fig. 231), as described in the chapter
on aquatic insects. In digging insects, the fore legs are expanded to
form shovel-like organs, notably in the mole-cricket (Fig. 64, E), in
which the fore tibia has some resemblance to the human hand, while
the tarsus and tibia are remarkably adapted for cutting roots, after
the manner of shears. The Scarabaeidae have fossorial legs, the anterior
tarsi of which are in some genera reduced {F) or absent; they are rudi-
ANATOMY AND PHYSIOLOGY
49
-tr
mentary in the female (G) of Phanceus carnifex and absent in the male
{H), and absent in both sexes of Deltochilum. Though females of
PhancBus lose their front tarsi by digging, the degenerate condition of
these organs cannot be attributed to the inheritance of a mutilation,
but may have been brought about by disuse; though no one has ex-
plained why the two sexes should differ in this
respect. Many insects use the legs to clean the
antennae, head, mouth parts, wings or legs; the
honey bee (with other bees, also ants, Carabidae,
etc.) has a special antenna cleaner on the front legs
(Fig. 267, D), which is described, with other inter-
esting modifications of the legs, on page 229.
Indeed, the legs serve many such minor pur-
poses in addition to locomotion. They are com-
monly used to hold the female during coition,
and in several genera of Dytiscidae (Dytiscus,
Cyhister) the male (Fig. 64, /) has tarsal disks and
cupules chiefly on the front tarsi, for this purpose.
tb
Fig. 62. — Leg of a beetle, Calo-
soma calidutn. c, coxa; cl, claws;
/, femur; s, spur; t^-t^, tarsal seg-
ments; tb, tibia; tr, trochanter.
Fig. 63. — Left hind leg of Bittacus.
c, coxa genuina; cm, epimeron; es,
episternum; /, femur; m, trochantin; t;
trochanter.
Among other secondary sexual peculiarities of the legs may be men-
tioned the tibial brushes of the male Catocala concumbens, regarded as
scent organs, and the queer appendages of male Dolichopodid^E that
dangle in the air as these flies perform their dances.
The pulvillus is commonly an adhesive organ. In flies it has glandu-
lar hairs that enable the insects to walk on smooth surfaces and to walk
upside down; so also in many beetles and notably in the honey bee (Fig.
65) ; in this insect the pulvillus is released rapidly from the surface to
which it has been applied, by rolling up from the edges inward.
Sense organs occur on the legs. Thus tactile hairs are almost
always present on these appendages, while auditory organs occur on
the front tibiae of Tettigoniidae, Grylhdae and some ants. Finally, the
so
ENTOMOLOGi'
legs may be used to produce sound, as in Stenohothrus and such other
Locustidae as stridulate by rubbing the femora against the tegmina.
Legs of Larvae.— Thoracic legs, terminating in a single claw, are
present in most larvae. Caterpillars have, in addition, fleshy abdominal
Fig. 64. — Adaptive modifications of the legs. A, Cicindela sexguttala; B, Nemobius
vittatus, hind leg; C, Stagmomantis Carolina, left fore leg; D, Pelocoris femoratus, right fore
leg; E, Gryllotalpa borealis, left fore leg; F, Canlhon lavis, right fore leg; G, PhancEus carnifex,
fore tibia and tarsus of female; H, P. carnifex, fore tibia of male; /, Dytiscus fascivenlris,
right fore leg of male; c, coxa;/, femur; s, spur; t, trochanter; tb, tibia; ts, tarsus.
legs (Fig. 64) ending in a circlet of hooks. Most caterpillars have five
pairs of these legs (on abdominal segments 3, 4, 5, 6, and 10), but the
ANATOMY AND PHYSIOLOGY
51
rest vary in this respect. Thus Lagoa has seven pairs (segments 2-7 and
10) and Geometridae two (segments 6 and 10), while a few caterpillars
{Tischeria, Limacodes) have none. Larvae of
saw flies (Tenthredinidae) have seven or eight
pairs of abdominal legs and larvae of most
Panorpidas, eight pairs. Not a few coleopter-
ous larvae (some Cerambycidac, Hypera) also
have abdominal tubercles that represent legs,
but are incompletely developed as compared
with those of Lepidoptera.
The legless, or apodous, condition occurs
frequently among larvae and always in correla-
tion with a sedentary mode of life; as in the
larvae of many Cerambycidae, almost all Rhyn-
chophora, a few Lepidoptera, all Diptera, and Fig. 65.— Foot of honey bee.
,, TT , 4-rr 4.U ^- -^ c- • ■ ^P^^ ■inellifera. c, c. claws; /..
all Hymenoptera except Ten thredmidae, Sirici- puiviiius; t^-t\ tarsal seg-
d«, and other Terebrantia. ments.-After Cheshire.
Among adult insects, female scale insects are exceptional in being
legless.
Walking. — An adult insect, when walking, normally uses its legs in
two sets of three each; thus the front and hind legs of one side and the
Fig. 66. — Caterpillar of Protoparce sexta. Natural size.
middle leg of the other move forward almost simultaneously — though
not quite, for the front leg moves a Httle before the middle one, which,
in turn, precedes the hind leg. During these movements the body is
supported by the other three legs, as on a tripod. The front leg,
having been extended and its claws fixed, pulls the body forward by
52
ENTOMOLOGY
means of the contraction of the tibial flexors; the hind leg, on the con-
trary, pushes the body, by the shortening of the tibial extensors,
against the resistance afforded by the tibial spurs; the middle leg acts
much like the hind one, but helps mainly to steady the body. Different
species * show different peculiarities of gait. In its analysis, the
walking of an insect is rather intricate, as Graber and Marey have shown.
The mode of action of the principal leg muscles may be gathered
from Fig. 67, Here the flexion of the tibia would cause the tibial spur
(s) to describe the line 51 ; and the backward movement of the leg due
to the upper coxal rotator r would cause the spur to follow the arc
53. As the resultant of both these movements, the path actually
ec //
Fig. 67. — Mechanics of an insect's leg. a, axis of coxa; c, coxa; cl, claw; e, extensor of
tibia; ec, extensor of claw; et, extensor of tarsus ;/, flexor of tibia ;/c, flexor of claw;//, flexor
of tarsus; r, r, rotators of coxa; 5, spur; t, trochanter muscle (elevator of femur) ; ti, tibia. —
After Graber.
described by the tibial spur is 5 2 ; then, as the leg moves forward, the
curve is continued into a loop.
Caterpillars use their legs successively in pairs, and when the pairs
of legs are few and widely separated, as in Geometridae, a curious looping
gait results.
The leg muscles of a cockroach are shown in Fig. 68.
Leaping. — The hind legs, inserted nearest the center of gravity, are
the ones employed in leaping, and they act together. A grasshopper
prepares to jump by bending the femur back against the tibia; to make
the jump, the tibia is jerked back against the ground, into which the
tibial spurs are driven, and the straightening of the leg by means of the
powerful extensors throws the insect into the air. At the distal end of
the femur are two lobes, one on each side of the tibia, which prevent
wobbling movements of the tibia.
ANATOMY AND PHYSIOLOGY
53
Wings. — The success of insects as a class is to be attributed largely
to their possession of wings. These and the mouth parts, surpassing all
the other organs as regards range of differentiation, have furnished the
best criteria for the purposes of classification. The wings of insects
present such countless differences that an expert can usually refer a
detached wing to its proper genus and often to its species, though no
fewer than four hundred thousand species of insects are already known.
Typically, there are two pairs of wings, at-
tached respectively to the mesothorax and the
metathorax, the prothorax never bearing wings,
as was said. When only one pair is present it is
almost invariably the anterior pair, as in Diptera
and male Coccidae, though in male Strepsiptera it
is the posterior pair, the fore wings being
rudimentary.
In bird lice, fleas and most other parasitic in-
sects, the wings have degenerated through disuse.
In Thysanura and Collembola there are no traces
of wings even in the embryo; whence it is inferred
that wings originated later than these orders of
insects.
M tiller and Packard have regarded the wings
as tergal outgrowths; Tower, however, has shown
that the wings of Coleoptera, Orthoptera and
Lepidoptera are pleural in origin, arising just below _
the line where later the suture between the pleuron left mid leg of a cock-
roach, posterior aspect.
abc, abductor of coxa;
adc, adductor of coxa; ef,
extensor of tibia; et, ex-
tensor of femur; /^ flexor
of tibia.; fta, flexor of tar-
sus; rl, retractor of tar-
sus.— After MiALL and
Denny.
and tergum will originate, though the wings may
subsequently shift to a more dorsal position.
Modifications of Wings. — Being commonly
more or less triangular, a wing presents three mar-
gins: front (costal), outer (apical) and inner (anal) ;
and three angles: humeral (at the base of the casta),
apical (at the apex of the wing) and anal (between outer and inner
margins). Various modifications occur in the front wings, which are
in many orders more useful for protection than for flight. Thus, in
Orthoptera, they are leathery, and are known as tegmina; in Coleoptera
they are usually horny, and are termed elytra; in Heteroptera, the base
of the front wing is thickened and the apex remains membranous,
forming a hemelytron. Diptera have, in place of the hind wings, a
pair of clubbed threads, known as balancers, or halteres, and male
54
ENTOMOLOGY
Scl
Coccidae have on each side a bristle that hooks into a pocket on the
wing and serves to support the latter. In many muscid flies a doubly
lobed membranous squama occurs at the base of the wing.
In Hymenoptera the front and hind wings of the same side are held
together by a row of hooks {hamuli); these are situated on the costal
margin of the hind wing and clutch a rod-like fold of the fore wing.
In very many moths, the two wings are enabled to act as one by means
of a frenulum, consisting of a spine or a bunch of bristles near the base
of the hind wing, which, in some forms, engages a membranous loop on
the fore wing.
In the generalized moths of the family Hepialidae, the overlapping
fore and hind wings are held together by SLJugum, projecting backward
from the base of the fore wing.
Venation, or Neuration. — A wing is divided by its veins, or nervures,
into spaces, or cells.
Sc2 „ . The distribution of the
veins is of great sys-
tematic importance,
but formerly, the ho-
mologies of the veins in
the different orders of
insects were not fixed,
so that no little con-
fusion resulted. For
example, the term dis-
cal cell, used in descriptions of Lepidoptera, Diptera, Trichoptera and
Psocidae, was in no two of these groups appHed to the same cell. The
admirable work of Comstock and Needham, however, seems to settle
this disputed subject. By a study of the tracheae which precede and,
in a broad way, determine the positions of the veins, these authors have
arrived at a primitive type of tracheation (Fig. 69) to which the more
complex types of tracheation and venation may be referred.
In general, the following principal longitudinal veins may be distin-
guished, in the following order: costa, suhcosta, radius, media, cubitus,
and anal (Figs. 69-73).
The costa (C) strengthens the front margin of the wing and is essen-
tially unbranched.
The subcosta {Sc) is close behind the costa and is unbranched in the
imagines of many orders in which there are few wing veins, though it is
typically a forked vein.
3dA 2dA
IstA
Cu2
Pig. 69. — Hypothetical type of venation. A, anal vein;
C, costa; Cu, cubitus; M, media; R, radius; Sc, subcosta. —
Figs. 69-73 after Comstock and Needham.
ANATOMY AND PHYSIOLOGY
55
The radius (R), though subject to much modification, is typically
five-branched, as in Fig. 69. The second principal branch of the
radius is termed the radial sector (Rs) .
The media (M) is often three-branched and is typically four-
branched, according to Comstock and Needham.
The cubitus (Cw) has two branches.
Fig. 70. — Wing of a fly, Rhyphus. Lettering as before.
The anal veins {A) are typically three, of which the first is usually
simple, while the second and third are many-branched in wings that
have an expanded anal area.
The Plecoptera, as a whole, show the least departure from the
primitive type of venation; which is well preserved, also, in the more
generalized genera of the Trichoptera.
Starting from the primitive type, specialization has occurred in two
ways: by reduction and by
addition. Reduction occurs £
either by the atrophy of veins
or by the coalescence of two
or more adjacent veins.
Atrophy explains the lack of
all but one anal vein in
Rhyphus (Fig. 70) and other
Diptera, and the absence of
the base of the media in vl wo- ^^^- ''^
sia (Fig. 71) and many other
Lepidoptera; in the pupa of Anosia, the media may be found com-
plete. Coalescence "takes places in two ways: first, the point at
which two veins separate occurs nearer and nearer the margin of the
wing, until finally, when the margin is reached, a single vein remains
where there were two before ; second, the tips of two veins may approach
each other on the margin of the wing until they unite, and then the
coalescence proceeds towards the base of the wing." (Comstock and
2dA
-Wing of a butterfly,
as before.
A nosia . Lettering
56
ENTOMOLOGY
Needham.) The former, or outward, kind of coalescence is common
in most orders of insects; the latter, or inward, kind is especially
prevalent in Diptera.
Speciahzation by addition occurs by a multiplication of the branches
of the principal veins, or by the development of secondary longitudinal
veins between these branches.
Comstock and Needham have succeeded in homologizing practically
all the types of neuration,
including such perplexing
types as those of Ephemerida
(Fig. 72), Odonata (Fig. 21,
B) and Hymenoptera (Fig.
73), and have established a
uniform terminology of the
wing veins. The system built
up during some twenty-five
years by Comstock and his fol-
lowers is embodied in his great
volume. The Wings of Insects.
A student of the subject of venation should consult the many articles
by Tillyard, a keen investigator, whose point of view is in some respects
different from that of Comstock and Needham. He holds, for example,
that the primitive type of wing had many veins instead of few, and
that the evolutionary tendency has been, generally speaking, toward a
reduction in the number of veins.
Fig. 72. — Wings of a May fly. Lettering as before.
Fig. 73. — A typical hymenopterous wing. Lettering
Folding of Wing. — In some beetles (as Chrysohothris) the wings are
no larger than the elytra and are not folded; in others the wings exceed
the elytra in size, and when not in use are folded under the elytra in
ways that are simple but efficient, as described by Kolbe and by Tower.
To be understood, the process of folding should be observed in the
living insect. As described by Tower for the Colorado potato beetle,
ANATOMY AND PHYSIOLOGY
57
the folded wing (Fig. 74, B) exhibits a costal joint (a), a fold parallel
to the transverse vein (b) , and a complex joint at d. The wing rotates
upon the articular head (ah) and when folded back beneath the wing-
covers the inner end of the cotyla (c) is brought into contact with a
chitinous sclerite of the thorax, which stops the further movement
of the cotyla medianward, and as the wing swings farther back the
middle system of veins (m) is pushed outward and anteriorly. This
motion, combined with the backward movement of the wing as a whole,
produces the folding of the
distal end of the wing. There
are no traces of muscles or
elastic ligaments in the wing
which could aid in the folding.
Mechanics of Flight. — The
mechanism of insect flight is
much less complex than one
might anticipate. Indeed,
owing to the structure of the
wing itself, simple up and
down movements are suffi-
cient for the simplest kind of
flight. During oscillation,
the plane of the wing changes,
as may be demonstrated by
holding a detached wing by
its base and blowing at right
angles to its surface ; the mem-
brane of the wing then yields
to the pressure of the air while
the rigid anterior margin does not, to any great extent. Similarly,
as the wing moves downward the membrane is inclined upward by the
resistance of the air, and as the wing moves upward the membrane
bends downward. Therefore, by becoming deflected, the wing encoun-
ters a certain amount of resistance from behind, which is sufficient to
propel the insect. The faster the wings vibrate, the greater the deflec-
tion, the greater the resistance from behind, and the faster the flight
of the insect.
The path traced in the air by a rapidly vibrating wing may be deter-
mined by fastening a bit of gold leaf to the tip of the wing and allowing
the insect — a wasp, for example — to vibrate its wings in the sunlight,
Fig. 74. — Wing of Leptinotarsa decemlineata. A,
spread; B, folded; a, costal joint; ah, articular head;
an, anterior system of veins; b, transverse vein; c,
cotyla; d, joint; in, middle system of veins; p, poste-
rior system of veins. — After Tower.
58
ENTOMOLOGY
against a dark background. Under these conditions, the trajectory
of the wing appears as a luminous elongate figure 8. During flight,
the trajectory consists of a continuous series of these figures, as in Fig.
75-
Marey, an authority on animal locomotion, used chronophotography,
among other methods, in studying the proc-
ess of flight, and obtained at first twenty,
and later one hundred and ten, successive
photographs per second of a bee in flight.
As the wings were vibrating 190 times per
second, however, the images evidently
-Trajectory of the wing represented isolated and not consecutive
of an insect. ^
phases of wing movement. Nevertheless,
the images could be interpreted without difficulty, in the light of
the results obtained by other methods. At length he obtained sharp
Fig.
of a second.
The frequency of wing vibration may be ascertained from the note
made by the wing— if it vibrates rapidly enough to make one; and, in
Pig. 76. — Records of wing vibration. A, mosquito. Anopheles. Above is the wing
record and below is the record of a tuning-fork which vibrated 264.6 times per second. B,
wasp, Polistes. The tuning-fork in this instance had a vibration frequency of 97.6.
any case, may be determined graphically by means of a kymograph,
which, in one of its forms, consists of a cylinder covered with smoked
paper and revolved by clockwork at a uniform rate. The insect is
held in such a position that each stroke of the wing makes a record on
the smoked paper, as in Fig. 76, A. Comparing this record with one
made on the same paper by a tuning-fork of known vibration period,
the frequency of wing vibration can be determined with great accuracy.
ANATOMY AND PHYSIOLOGY
59
As the wing moves in the arc of a circle, the radius of which is the length
of the wing, the extreme tip of the wing records only a short mark; if,
however, the wing is pressed against the smoked cylinder, a large part
of the figure-8 trajectory may be obtained, as in Fig. 76, B. The wings
of the two sides move synchronously, as Marey found.
The smaller the wings are, the more rapidly they vibrate. Thus a
butterfly {P. rapce) makes 9
strokes per second, a dragon
fly 28, a sphingid moth 72, a
bee 190 and a house fly 330.
Wing Muscles. — The base
of a wing projects into the
thoracic cavity and serves for
the insertion of the direct
muscles of flight. Regarding
the wing as a lever (Fig. 77,
A) with the fulcrum at p, it
is easy to understand how the
contraction of muscle e raises
the wing and that of muscle d
lowers it. These muscles are
shown diagrammatically in Fig.
77, B. Besides these, there
are certain muscles of flight
which act indirectly upon the ,^'^- 'Z--^- ^fSra^a to illustrate the action
J ^ of the wing muscles of an insect. B, diagram of
wings, by altering the form of wing muscles, a, alimentary canal; cm. muscle
11 . ,, rpi ,1 for contracting the thorax, to depress the wings;
tne tnOraClC wall. inUS trie ^^ depressor of wing; e, elevator of wing; ex,
muscle id (Fis 77 B) elevates ^^^cle for expanding the thorax, to elevate the
wings; id, indirect depressor; ie, indirect elevator;
the wing by pulling the tergum /. leg muscle; p, pivot, or fulcrum; s. sternum; t,
toward the sternum; and the tergum; ^g. wing.-After Graber.
longitudinal muscle id depresses the wing indirectly by arching the ter-
gum of the thorax.
Though up and down movements are all that are necessary for the
simplest kind of insect flight, the process becomes complex in proportion
to the efl&ciency of the flight. Thus in dragon flies there are nine
muscles to each wing: five depressors, three elevators and one adductor.
The earlier accounts of the mechanics of flight by Marey and others
have been modified and improved upon by Stellwaag and by Ritter,
whose modern methods of investigation have added considerably to our
knowledge of the subject. These later authors have shown, particu-
larly, the parts played by the thoracic sclerites during flight.
6o ENTOMOLOGY
The development of aviation was due largely to thorough studies
of the flight of birds and insects.
Abdomen. — The chief functions of the abdomen are respiration and
reproduction, to which should be added digestion. The abdomen as a
whole has undergone less differentiation than the thorax and presents a
simpler and more primitive segmentation.
Segments. — A typical abdominal segment bears a dorsal plate, or
tergum (notum) and a ventral plate, or sternum, the two being connected
by a pair of pleural membranes, which facilitate the respiratory move-
ments of the tergum and sternum. Abdominal tergites and sternites
are often termed urotergites and urosternites, respectively. Most of
the abdominal segments have spiracles, one on each side, situated in or
near the pleural membranes of the first seven or eight segments. The
total number of pairs of spiracles is as follows:
Thoracic Abdominal Total
Campodea 2 i 3
Japyx^ 4 7 II
Machilis 2 7 9
Lepisma 2 8 10
Nicoletia. • 2 8 10
Orthoptera 2 8 10
Odonata 2 8 10
Heteroptera 2 6(7) 8(9)
Lepidoptera 2 7 9
Diptera 2 7 9
1 Japyx actually has four thoracic and seven abdominal spiracles, as described and
illustrated by Grassi (1888), Willem (1900) and Verhoeff (1904); a study of their figures
indicates, however, that the spiracles may have migrated forward, and that the fourth
thoracic pair (there being two pairs in the metathorax) belongs morphologically to the
first abdominal segment.
Number of Abdominal Segments. — Though only ten abdominal
segments are evident in many adult insects and many larvae as well,
the typical number is eleven, and the maximum twelve. In embryos of
Thysanura, Orthoptera, Ephemerida, Odonata, Coleoptera and Hy-
menoptera, eleven abdominal neuromeres (primitive ganglia) have been
found by Heymons and others; each neuromere representing a segment;
and the twelfth segment is present as a telson, a terminal, segment con-
taining the anus, but without a neuromere and never bearing a pair of
appendages. This telson is present also in the adults of some generalized
insects, as Orthoptera. In the more specialized orders, ten may usually
be distinguished, with more or less difiiculty, though the number is
apparently, and in some cases actually, less owing to modifications of
ANATOMY AND PHYSIOLOGY
6l
the base of the abdomen in relation to the thorax, but especially to
modifications of the extremity of the abdomen, for sexual purposes.
Modifications. — In aculeate Hymenoptera the first segment of the
abdomen has been transferred to the thorax, where it is known as the
propodeiim, or median segment; in other words, what appears to be the
first abdominal segment is actually the second; this, as in bees and
wasps, often forms a petiole, which enables
the sting to be applied in almost any direc-
tion. In Cynipidae the tergum of segment
two or three occupies most of the abdom-
inal mass, the remaining segments being
reduced and inconspicuous. The terminal
segments of the abdomen often telescope
into one another, as in many Coleoptera and
Hymenoptera (Chrysididae), or undergo
other modifications of form and position
which obscure the segmentation. As to
the number of evident (not actual) abdom-
inal segments, Coleoptera show five or six
ventrally and seven or eight dorsally;
Lepidoptera, seven in the female and eight
in the male; Diptera, nine (male Tipulidae)
or only four or five; and Hymenoptera, nine
(Tenthredinidas) or as few as three (Chry-
sididae). In the larvae of these insects,
nine or ten abdominal segments are usually
distinguishable, though the tenth is fre-
quently modified, being in caterpillars
united with the ninth. Fig. 78.— Ventral aspect of the
. J -nv !• 1 1 • 1 abdomen of a female Machilis
Appendages.— Rudimentary abdommal maritima, to show rudimentary
limbs occur in Thysanura {Machilis, Fig. (^h^e^SJ apSSeVf'^tL*^^^^^^
78). Functional abdominallegS do not occur segment is omitted.) c, c, c, lateral
11, • iT_j.*i ^1. 1.J cerci and median pseudocercus. —
m adult msects, but m larvae the abdom- p^^^^ qudemans.
inal rolegs (Fig. 66) are homologous
with the thoracic legs and the other paired segmental appendages, as
the embryology shows. The embryo of (Ecanthus, according to Ayers,
has ten pairs of abdominal appendages (Fig. 199), equivalent to the
thoracic legs. Most of these embryonic abdominal appendages are
only transitory, but the last three pairs frequently persist to form the
genitalia, as in Orthoptera (to which order (Ecanthus belongs). In
62 ENTOMOLOGY
Collembola, the embryo has paired abdominal limbs, and those of the
first abdominal segment eventually unite to form the peculiar ventral
tube (Fig. 13) of these insects, while those of the fourth segment form
the characteristic leaping organ, or fur cula, and those of the third, the
tenaculum.
Cerci. — In many of the more generalized insects the abdomen bears
at its extremity a pair of appendages termed cerci. These occur in
both sexes and are frequently long and multiarticulate, as in Thysanura
(Figs. 78, 10, 11), Plecoptera (Fig. 19) and Ephemerida (Figs. 20, B;S6)
though shorter in cockroaches and reduced to a single sclerite in Locus-
tidae (Fig. 89). The paired cerci, or cercopoda of Packard, are usually
though not always associated with the eleventh abdominal segment and
are homologous with legs, as Ayers has found in (Ecanthus and Wheeler
in Xiphidium. As to their function, the cerci of Thysanura are tactile,
and those of the cockroach olfactory, while the cerci of male Locustidae
often serve to hold the female during copulation.
The so-called "median cercus" or "filum terminale" of Thysanura
(Figs. II, 78) and Ephemerida (Fig. 86) resembles the true cerci of
these insects in being multiarticulate and usually long, and in having the
same function; but differs from these morphologically in arising as a
median dorsal prolongation of the eleventh abdominal segment; being
therefore not equivalent to one of the paired segmental appendages.
For this median filament the term pseudocercus is appropriate.
Extremity of Abdomen. — Various modifications of the terminal
segments of the abdomen occur for the purposes of defecation and
especially reproduction. The anus, dorsal in position, opens always
through the last segment and is often shielded above by a suranal plate
and on each side by a lateral plate. The genital orifice is always ventral
in position and occurs commonly on the ninth abdominal segment,
though there is some variation in this respect. The external, or
accessory, organs of reproduction are termed the genitalia.
Female Genitalia. — In Neuroptera, Coleoptera, Lepidoptera and
Diptera the vagina simply opens to the exterior or else with the anus
into a common chamber, or cloaca. Often, as in Cerambyx (Fig. 79)
and Dasyneura (Fig. 80) the attenuated distal segments of the abdomen
serve the purpose of an ovipositor; thus in Itonididae, the terminal
segments, telescoped into one another when not in use, form when
extruded a lash-like organ exceeding frequently the remainder of the
body in length.
A true ovipositor occurs in Thysanura, Orthoptera, Odonata, Hemip-
ANATOMY AND PHYSIOLOGY
63
tera, Hymenoptera and some other orders of insects. The ovipositor
consists essentially of three pairs of valves, or gonapophyses — a dorsal, a
ventral and an inner pair. The two inner valves form a channel through
which the eggs are conveyed. In Tettigoniidai (Fig. 81) the three
J ^ 5 ^ valves of each side are held to-
gether by tongues and grooves,
which, however, permit sliding
Fig. 79. — Abdomen of female beetle, Cer-
ambyx, in which the last three segments are
used as an ovipositor. — After Kolbe.
Fig. 80. — Abdomen of a female midge,
Dasyneura leguminicola, to show the
pseudo -ovipositor.
movements to take place. Most authorities have found that the
gonapophyses belong to the segmental series of paired appendages —
are homodynamous with limbs — and pertain commonly to abdominal
Fig. 81. — Ovipositor of Phasgonura. — A, lateral aspect; B, ventral aspect; C, transverse
section; c, cerci; d, dorsal valve; i, inner valve; v, ventral valve. The numbers refer to ab-
dominal segments. — After Kolbe and Dewitz.
segments eight, nine and ten; though there are different views in
regard to this.
The ovipositor attains its greatest complexity in Hymenoptera, in
which it becomes modified for sawing, boring or stinging. In Sirex (Fig.
64
ENTOMOLOGY
82) the inner valves are united; in Apis the dorsal valves are represented
by a pair of palpi, the inner valves unite to form the sheath (Fig. 83, B),
and the ventral two form the darts, each of which has ten barbed teeth
behind its apex, which tend to prevent the with-
drawal of the sting from a wound. The action of
the sting, as described by Cheshire, is rather com-
plex. Briefly, the sheath serves to open a wound
and to guide the darts; these strike in alternately,
interrupted at intervals by the deeper plunging of
the sheath (Fig. 83, A). The poison of the honey
bee is secreted by two glands, one acid and the
other alkaline. The former (Fig. 84) consists of a
glandular region which secretes formic acid, of a
reservoir, and a duct that empties its contents into
the channel of the sheath. The alkaline gland also opens into the reser-
voir. It is said that both fluids are necessary for a deadly effect; and
that in insects which simply paralyze their
prey, as the solitary wasps, the alkaline
glands are functionless.
Fig. 82. — Cross-sec-
tion of the ovipositor of
Sir ex. c, channel; d,
d, dorsal valves; i,
united inner valves; v,
V, ventral valves.— After
Taschenberg
Fig. 83. — Sting of honey bee. A, i, 2, 3, posi-
tions in three successive thrusts; s, sheath. B,
cross-section; c, channel; i, united inner valves,
forming the sheath; v, v, ventral valves, or darts. —
A, after Cheshire; B, after Penger.
Fig. 84. — Sting and poison appara-
tus of honey bee. ag, accessory gland ;
p, palpus; pg, poison gland (formic
acid); r. reservoir; s, sting. — After
Kraepelin.
Male Genitalia. — The penis may be hollow or else solid, and in the
latter case the contents of the ejaculatory duct are spread upon its
surface. Morphologically, the male gonapophyses correspond to those
of the female. The penis (Fig. 85) represents the two inner valves of
the ovipositor and is frequently enclosed by one or two pairs of valves.
ANATOMY AND PHYSIOLOGY
6S
In Ephemerida the two inner valves are partly or entirely separate
from each other, forming two intromittent organs (Fig. 86) .
In male Odonata, the ejaculatory duct opens on the ninth abdominal
segment, but the copulatory organ is placed on the under side of the sec-
ond segment, to which the spermatozoa are transferred by the bending
of the abdomen. At copulation, the abdominal claspers of the male
grasp the neck of the female, and the latter bends her abdomen forward
until the tip reaches the pecuHar copulatory apparatus of the male.
The claspers of the male consist of a single pair, variously formed.
They are present in Ephemerida, Neuroptera, Trichoptera, Lepidoptera
(Fig. 87), Diptera and some Hymenoptera, though not in Coleoptera,
and often afford good specific characters, as in Odonata. In butterflies
of the genus Thanaos, the claspers are pecuHar in being strongly
asymmetrical. In Odonata (Fig. 88, A) and Orthoptera (Fig. 89, A)
the superior appendages of the male often serve as claspers.
In many insects the tergum of the last abdominal segment forms a
small suranal plate (Fig. 89, B, sp); this sometimes supplements the
claspers of the male in their function, as in Lepidoptera (Fig. 87, A, s).
2. Integument
Insects excel all other animals in respect to adaptive modifications of
the integument. No longer a simple limiting membrane, the integu-
FiG. 85. — Extremity of abdomen of a
male beetle, Hydrophilus, ventral aspect, g,
genitalia; p, penis; v^, v', pairs of valves
enclosing the penis; 6-9, sterna of abdominal
segments. — Aiter Kolbe.
'■■-.A^
1:
H
1
c
\
c M
\\ ^
m
B
Fig. 86. — Extremity of abdomen of a
male May fly, Hexagenia variabilis, ventral
aspect, c, c, c, cerci and pseudocercus (medi-
an); cl, cl, claspers; i, i, intromittent organs.
ment has become hardened into an external skeleton, evaginated to
form manifold adaptive structures, such as hairs and scales, and
66
ENTOMOLOGY
invaginated, along with the underlying cellular layer, to make glands of
various kinds.
Chitin. — The skin, or cuticula,^ of an insect differs from that of a
worm, for example, in being thoroughly permeated with a pecuHar sub-
stance known as chitin — the basis of the arthropod skeleton. This is a
Fig. 87. — Genitalia of a moth, Samia cecropia. A, male; B, female; a, anus; c, c,
claspers; o, opening of common oviduct; p, penis; 5, uncus (the doubly hooked organ);
V, vestibule, into which the vagina opens. The numbers refer to abdominal segments.
substance of remarkable stability, for it is unaffected by almost all ordi-
nary acids and alkalies, though it is soluble in sodic or potassic hypo-
chlorite (respectively, Eau de Labarraque and Eau de Javelle) and
yields to boihng sulphuric acid. If kept for a year or so under water,
Pig. 88. — Terminal abdominal appendages of a dragon fly, Plathemis tri?naculala. A,
male; B. female, i, inferior appendage; 5, s, superior appendages. The numbers refer to
abdominal segments.
however, chitin undergoes a slow dissolution, possibly a putrefaction,
which accounts in a measure for the rapid disappearance of insect
skeletons in the soil (Miall and Denny). By boiling the skin of an
insect in potassic hydroxide it is possible to dissolve away the cuticular
framework, leaving fairly pure chitin, without destroying the organized
1 The cuticula of an insect should be distinguished from the cuticle of a vertebrate, the
former being a hardened fluid, while the latter consists of cells themselves, in a dead and
flattened condition.
ANATOMY AND PHYSIOLOGY
67
form of the integument, though less than half the weight of the integu-
ment is due to chitin. The formula of chitin is given as CgHuNOa or
C18H15NO12 by Krukenberg, and many adopt the formula C15H26N2O10;
though no two chemists agree as to the exact proportions of these
elements, owing probably to variations in the substance itself in differ-
89 10 11
Fig. 89. — Extremity of the abdomen of a grasshopper, Melanoplns differenlialis. A,
male- B, female. The terga and sterna are numbered, c, cercus; d, dorsal valves of ovi-
positor; e, egg guide; p, podical plate; s, spiracle; sp, suranal plate; v. ventral valves of
ovipositor.
ent insects or even in the same species of insect. Iron, manganese and
certain pigments also enter into the composition of the integument.
Chitin is not peculiar to arthropods, for it has been detected in the
set£e and pharyngeal teeth of annelid worms, the shell of Lingula and the
pen of the cuttle fish (Krukenberg) .
The chitinous integument (Fig. 90) of most insects consists of two
layers: (i) an outer layer, homogeneous, dense,
without lamellae or pore canals, and being the
seat of the cuticular colors; (2) an inner layer,
"thickly pierced with pore canals, and always
in layers of different refractive indices and differ-
ent stainability." (Tower.) These two layers,
respectively primary and secondary cuticula, are
radically different in chemical and physical prop-
erties.
from the hypodermis cells, the primary cuticula ^X^cutic™!!'*:^"::
being the first to form and harden. dermis cell; n, nucleus.' —
The fluid that separates the old from the new ^^*" Tower.
cuticula at ecdysis is poured over the hypodermis by certain large special
cells, which, according to Tower, "are not true glands, but the setiger-
ous cells which, in early Hfe, are chiefly concerned with the formation
of the hairs upon the body; but upon the loss of these, the cell takes
on the function of secreting the exuvial fluid, which is most copious at
Fig. 90. — Section
through integument of a
^ , , . n •! -• beetle, Chrysobothris. b.
Each layer arises as a fluid secretion basement membrane; cK
68
ENTOMOLOGY
pupation. These cells degenerate in the pupa, and take no part in the
formation of the imaginal ornamentation."
\
Fig. 91. — Modifications of the hairs of bees. A, B, Megachile; C, E, F, Colletes; D, Chelos'
toma. — After Saunders.
I
Histology. — The chitinous cuticula owes its existence to the activity
of the underlying layer of hypodermis cells (Fig. 90), a single layer,
Pig. 92. — Section of antenna of a moth,
Salurnia, to show developing hairs, c, cutic-
ula; /, formative cell, or trichogen, of hair;
h, hypodermis; t, trachea. — After Semper.
Fig. 93. — Radial section through the
base of a hair of a caterpillar, Pieris rapce.
c, cuticula; /, formative cell, or trichogen;
h, hair; hy, hypodermis.
Ectodermal in origin. These cells, distinct in embryonic and often in
early larval life, subsequently become confluent by the disappearance
6i the intervening cell walls, though each cell is still indicated by its
ANATOMY AND PHYSIOLOGY
69C
nucleus. The cells are limited outwardly by the cuticula and inwardly,
by a delicate, hyaline basement membrane; they contain pigment granules,'
fat-drops, etc.
Externally the cuticula may be smooth, wrinkled, striate, granulate,:
tuberculate, or sculptured in numberless other ways; it may be shaped
into all manner of structures, some of which are clearly adaptive, while
others are unintelligible.
Hairs, Setae and Spines. — These occur universally, serving a great
variety of purposes; they are not always simple in form, but are often
toothed, branched or otherwise modified
(Fig. 91) . Hairs and bristles are frequently
tactile in function, over the general integu-
ment or else locally; or olfactory, as on the
antennae of moths; or occasionally auditory,
as on the antennae of the male mosquito;
these and other sensory modifications are
described beyond. The hairy clothing of
some hibernating caterpillars (as Isia isa-
bella) probably protects them from sudden
changes of temperature. Hairs and spines
frequently protect an insect from its enemies,
especially when these structures are glandu-
lar and emit a malodorous, nauseous or
irritant fluid. Glandular hairs on the pul-
villi of many flies, beetles, etc., enable these
insects to walk on slippery surfaces. The
twisted or branched hairs of bees serve to
. 1111 11 • • 1 ^ ^J^- 94-— Vanous forms of
gather and hold pollen grams; m short, scales. A,E,thysa.nnTan,Machi-
these simple structures exhibit a surprising ^;^:^SJ::^X:SXi^c^S.
variety of adaptive modifications, many of
which will be described in connection with other subjects.
A hair arises from a modified hypodermis cell, formative cell or
trichogen (Fig. 92), the contents of which extend through a pore canal
into the interior of the hair (Fig. 93) ; sometimes, to be sure, as in
glandular or sensory hairs, the hair cell is multinucleate, representing,
therefore, as many cells as there are nuclei. The wall of a hair is
continuous with the general cuticula and at moulting each hair is
stripped off with the rest of the cuticula, leaving in its place a new hair,
which has been forming inside the old one.
Scales. — Besides occurring throughout the order Lepidoptera and
in numerous Trichoptera, scales are found in many Thysanura and
70
ENTOMOLOGY
Fig. 95. — Cross-section of scale
Anosia. — After Mayer.
Collembola, several families of Coleoptera (including Dermestidae,
Cerambycidae and Curculionidae) , a few Diptera and a few Psocidae.
Though diverse in form (Fig. 94) , scales are essentially flattened sacs
having at one end a short pedicel for attachment to the integument.
The scales usually bear markings, which are more or less characteristic
of the species; these markings, always
minute, are in some species so exqui-
sitely fine as to test the highest powers
of the microscope; the scales of certain
Collembola {Lepidocyrtus, etc.) have long
been used, under the name of " Podura " scales, to test the resolving power
of objectives, for which purpose they are excelled only by some of the
diatoms. Butterfly scales are marked with parallel longitudinal
ridges (Fig. 94, C), which are confined almost entirely to the upper, or
exposed, surface of the scale (Fig. 95) and number from 33 or less
(Anosia) to 1,400 {Morpho) to each scale, the striae being in the latter
genus from .002 mm. to .0007 mm.
apart (Kellogg) ; between these longi- ^ ^ ^ (
tudinal ridges may be discerned
delicate transverse markings. Inter-
nally, scales are hollow and often
contain pigments derived from the
blood.
On the wing of a butterfly the
scales are arranged in regular rows and
overlap one another, as in Fig. 96 ; in
the more primitive moths and in Tri-
choptera, however, their distribution
is rather irregular.
A scale is the equivalent of a hair,
for (l) a complete series of transitions ^^^- 96.— Arrangement of scales on the
- , . , , wing of a butterfly, Papilio.
from hairs to scales may be found on
a single individual (Fig. 97) ; and (2) hairs and scales agree in their man-
ner of development, as shown by Semper, Schaffer, Spuler, Mayer and
others. Both hairs and scales arise as processes from enlarged hypo-
dermis cells, or formative cells (Fig. 98). The scale at first contains
protoplasm, which gradually withdraws, leaving short chitinous strands
to hold the two membranes of the scale together.
Uses of Scales. — Among Thysanura and Collembola, scales occur
only on such species as live in comparatively dry situations, from which
ANATOMY AND PHYSIOLOGY
71
it may be inferred that the scales serve to retard the evaporation of mois-
ture through the delicate integument of these insects. This inference is
Fig. 97. — Hairs and scales of a moth, Samia cecropia.
supported by the fact that none of the scaleless Collembola can live long
in a dry atmosphere; they soon shrivel and die even under conditions
Fig. 98. — Development of butterfly scales. FiG. 99. — Androconia of butterflies. A,
A. Vanessa; B, Anosia. 6, basement mem- Pieris rapm; B, Everes comyntas.
brane; /, formative cell; h, hypodermis; s,
scale. — After Mayer.
of dryness which the scaled species are able to withstand. In Lepidop-
tera the scales are possibly of some value as a mechanical protection;
72
ENTOMOLOGY
they have no injfluence upon flight, as Mayer has proved, and appear to
be useful chiefly as a basis for the development of color and color
patterns — which are not infrequently adaptive.
Androconia. — The males of many butterflies, and the males only,
have peculiarly shaped scales known as androconia (Fig. 99) ; these are
commonly confined to the upper surfaces of the front wings, where they
are mingled with the ordinary scales or else are disposed in special
patches or under a fold of the costal margin of the wing (Thanaos).
The characteristic odors of male butterflies have long been attributed
to these androconia, and M. B. Thomas has found that the scales arise
Fig. 100. — Section across tarsus of a beetle,
Hylobius, to show bulbous glandular hairs. —
After SiMMERMACHER.
Fig. ioi. — Stinging hair of a caterpillar,
Gaslropacha. c, cuticula; g, gland cell; h,
hair; hy, hypodermis. — After Claus.
from glandular cells, which doubtless secrete a fluid that emanates
from the scale as an odorous vapor, the evaporation of the fluid being
facilitated by the spreading or branching form of the androconium.
Similar scales occur also on the wings of various moths and some
Trichoptera {Mystacides) .
Glands. — A great many glands of various form and function have
been found in insects. Most of these, being formed from the hypoder-
mis, may logically be considered here, excepting some which are inti-
mately concerned with digestion or reproduction.
Glandular Hairs and Spines. — The presence of adhesive hairs on
the empodium of the foot of a fly enables the insect to walk on a smooth
surface and to walk upside down; these tenent hairs emit a transparent
sticky fluid through minute pore canals in their apices. The tenent
hairs of Hylobius (Fig. 100) are each supplied with a flask-shaped unicel-
lular gland, the glutinous secretion of which issues from the bulbous
ANATOMY AND PHYSIOLOGY 73
extremity of the hair. Bulbous tenent hairs occur also on the tarsi of
Collembola, Aphididas and other insects.
Nettling hairs or spines clothe the caterpillars of certain Saturniida)
{Automeris), Liparidae, etc. These spines (Fig. loi), which are sharp,
brittle and filled with poison, break to pieces when the insect is handled
and cause a cutaneous irritation much like that made by nettles. In
Lagoa crispata (Fig. 102) the irritating fluid 'is secreted, as is usual, by
several large hypodermal cells at the base of each spine. These irritating
hairs protect their possessors from almost all birds except cuckoos.
Repellent Glands. — The various offensive fluids emitted by insects
are also a highly effective means of defense against birds and other in-
sectivorous vertebrates as well as against predace-
ous insects. The blood itself serves as a repellent
fluid in the oil-beetles (Meloidae) and Coccinellidae,
issuing as a yellow fluid from a pore at the end of
the femur. The blood of Meloidae (one species of
which is still used medicinally under the name of
''Spanish Fly") contains cantharidine, an extremely
caustic substance, which is an almost perfect pro-
tection against birds, reptiles and predaceous insects.
Coccinellidae and Lampyridae are similarly exempt from
attack. Larvae of Cimbex when disturbed squirt
jets of a watery fluid from glands opening above the Fig. 102.— sting-
spiracles. Many Carabid^ eject a pungent and often ':^:!Z^:S^_
corrosive fluid from a pair of anal glands (Fig. —After Packard.
148); this fluid in Brachinus, and occasionally
in Galerita janus and a few other carabids, volatilizes explosively
upon contact with the air. When one of these ''bombardier-beetles"
is molested it discharges a puff of vapor, accompanied by a distinct
report, reminding one of a miniature cannon, and this performance
may be repeated several times in rapid succession; the vapor is acid and
corrosive, staining the human skin a rust-red color. Individuals of a
large South American Brachinus when seized "immediately began to
play off their artillery, burning and staining the flesh to such a degree
that only a few specimens could be captured with the naked hand,
leaving a mark which remained for a considerable time." (Westwood.)
As malodorous insects, Hemiptera are notorious, though not a few
hemipterous odors are (apart from their associations) rather agreeable
to the human olfactory sense. Commonly the odor is due to a fluid
frorfi a mesothoracic gland or glands, opening between the hind coxae.
74
ENTOMOLOGY
Eversible hypodermal glands of many kinds are common in larvae of
Coleoptera and Lepidoptera. The larvae of Lina lap_ponica, among
other Chrysomelidae, evert numerous paired vesicles which emit a
peculiar odor. The caterpillars of our Papilio butterflies, upon being
irritated, evert from the prothorax a yellow Y-shaped osmeterium (Fig.
0 <■:
Pig. 103. — Osmeterium of Papilio Pig. 104.— Ventralaspectofworke^honeybee,show-
/)oZy«:en«. ing the four pairs of wax scales. — After Cheshire.
103) which diffuses a characteristic but indescribable odor that is
probably repellent. The larva of Cerura everts from the under side of
the neck a curious spraying apparatus which discharges formic acid.
^ Alluring Glands.^Odors are
'■• ' largely used among insects to
attract the opposite sex. The
androconia of male butterflies
have already been spoken of.
Males of Catocala concumhens dis-
seminate an alluring odor from
scent tufts on the middle legs.
Female saturniid moths (as cecro-
pia and promethea) entice the
males by means of a characteris-
tic odor emanating from the ex-
tremity of the abdomen. In
lycaenid caterpillars, an eversible
sac on the dorsum of the seventh abdominal segment secretes a sweet
fluid, for the sake of which these larvae are sought out by ants.
Wax Glands. — Wax is secreted by insects of several orders, but es-
pecially Hymenoptera and Hemiptera. In the worker honey bee the
wax exudes from unicellular hypodermal glands and appears on the
Fig. 105. — Head of caterpillar of Samia
cecropia. a, antenna; c, clypeus; I, labrum;
Ip, labial palpus; m, mandible; mp, maxillary
palpi; o, ocelli; s, spinneret.
ANATOMY AND PHYSIOLOGY 75
under side of the abdomen as four pairs of wax scales (Fig. 104), on
the last four of the six evident segments of the abdomen (Dreyling).
Plant lice of the genus Schizoneura owe their woolly appearance to dense
white filaments of wax, which arise from glandular hypodermal cells.
In scale insects, waxen threads, emerging from cuticular pores, become
matted together to form a continuous shield over and often under the
insect itself, the cast skins often being incorporated into this waxen
scale. The wax glands in Coccidae are simply enlarged hypodermis
cells.
Some coccids produce wax in quantities sufficient for commercial
use. Thus species of Ceroplastes (and certain fulgorids as well) in
India and China yield a white wax that is used for making candles and
for other purposes.
The lac-insect, Tachardia lacca, of India, a scale insect Uving on
more than ninety species of trees and shrubs {Acacia, Ficus, Zizyphus,
etc.), furnishes the lac from which shellac, lacquer and other varnishes
are made. The raw lac is the scale, or shell, of the female insect (the
male producing scarcely any lac) and consists of a yellow to reddish
brown resinous exudation containing considerable wax, along with the
cast skins of the insect. From this material the commercial products
are extracted.
Silk Glands.^Larvae of very diverse orders spin silk, for the purpose
of making cocoons, webs, cases, and supports of one kind or another.
Silk glands, though most characteristic of Lepidoptera and Trichoptera,
oceur also in the cocoon-spinning larvae of not a few Hymenoptera
(saw flies, ichneumons, wasps, bees, etc.), in Diptera (Itonididae),
Siphonaptera, Neuroptera (Chrysopidae, Myrmeleonidae) , and in
various larvae whose pupae are suspended from a silken support, as in
the coleopterous families Coccinelhdae and Chrysomelidae (in part)
and the dipterous family Syrphidae, as well as most diurnal Lepidoptera.
The silk glands of caterpillars are homologous with the true saHvary
glands of other insects, opening as usual through the hypopharynx,
which is modified to form a spinning organ, or spinneret (Fig. 105).
The silk glands of Lepidoptera are a pair of long tubes, one on each side
of the body, but often much longer than the body and consequently
convoluted. Thus in the silk worm {Bomhyx mori) they are from four
to five times as long as the body and in Telea polyphemus, seven times
as long. In the silk worm the convoluted glandular portion of each
tube (Fig. 106) opens into a dilatation, or silk reservoir, which in turn
empties into a slender duct, and the two ducts join into a short common
7-6
ENTOMOLOGY
duct, which passes through the tubular spinneret. Two divisions of
the spinning tube are distinguished: (i) a posterior muscular portion, or
thread-press and (2) an anterior directing tube. The thread-press com-
bines the two streams of silk fluid into one, determines the form of the
silken thread and arrests the emission of the thread at times, besides
having other functions. The silk fluid hardens rapidly upon exposure
to the air; about fifty per cent, of the fluid
is actual silk substance and the remainder
consists of protoplasm and gum, with traces
of wax, pigment, fat and resin.
( Fig. 106. — Silk glands of the
silk worm, Bombyx mori. cd,
common duct; d, one of the
paired ducts; g, g, Filippi's
glands; gl, gland proper; p,
thread press; r, reservoir.
Fig. 107. — Sections of silk gland of the silk worm.
A, radial; B, transverse, b, basement membrane; i,
intima; 5, glandular cell with branched nucleus. —
After Helm.
A transverse or radial section of a silk gland shows a layer of glandu-
lar epithehal cells, with the usual intima and basement membrane (Fig.
107) ; the cells are remarkably large and their nuclei are often branched;
the intima is distinctly striated, from the presence of pore-canals. The
glands arise as evaginations of the pharynx (ectodermal) and the chi-
tinous intima of each gland is cast at each moult, along with the general
integument.
ANATOMY AND PHYSIOLOGY
7.7
The silk glands of caddis worms (Trichoptera) are essentially like
those of caterpillars (Lepidoptera) but the glands of Neuroptera
{Chrysopa, Myrmeleon, etc.) Coccinellidae, Chrysomelidae and Syrphidae,
which open into the rectum, are morphologically quite different frorti
those of Lepidoptera.
3. Muscular System
The number of muscles possessed by an insect is surprisingly large.
A caterpillar, for example, has about two thousand.
The muscles of the trunk are segmentally arranged — most evidently
abc
Fig. 108. Fig. 109. Fig. iio.
Muscles of cockroach; of ventral, dorsal and lateral walls, respectively, a, alary muscle;
abc, abductor of coxa; adc, adductor of coxa; ef, extensor of femur; h, head muscles; Is,
longitudinal sternal; It, longitudinal tergal; Ith, lateral thoracic; os, oblique sternal; ot,
oblique tergal; ts, tergo-stemal; ts^, first tergo-sternal. After Miall and Denny.
SO in the body of a larva or the abdomen of an imago, where the muscu-
lature is essentially the same in several successive segments. In the
thoracic segments of an imago, however, the musculature is, at first
sight, unlike that of the abdomen, and in the head it is decidedly-
different; though future studies will doubtless show that the thoracit
and cephalic kinds of musculature are only modifications of the simplet
abdominal type — modifications brought about in relation to the needs
of the legs, wings, mouth parts, antennse and other movable structures.
The muscular system has been generally neglected by students of
insect anatomy; the only comprehensive studies upon the subject being
78
ENTOMOLOGY
^ii
m
^^
Striated muscle chitinous tendons
fiber of an insect.
each of which has
those of Straus-Diirckheim (1828) on the beetle Melolontha; Lyonet
(1762), Newport (1834) and Lubbock (1859) on caterpillars; Lubbock
and Janet on Hymenoptera; Bauer (1910) on Dytiscus; and Berlese
(1909-13) on various insects.
The more important muscles in the body of a cockroach
are represented in Figs. 108-110, from Miall and Denny.
The longitudinal sternals with the longitudinal tergals act
to telescope the abdominal segments; the oblique ster-
nals bend the abdomen laterally; the ter go sternals, or
vertical expiratory muscles, draw the tergum and sternum
together. The muscles of the legs and the wings have
already been referred to.
Structure of Muscles. — The muscles of insects differ
greatly in form and are inserted frequently by means of
A muscle is a bundle of long fibers,
an outer elastic membrane, or
sarcolemma, within which are several nuclei; thus the fiber represents
several cells, which have become confluent. With rare exceptions
("alary" muscles and possibly a few thoracic muscles) the muscle fibers
of an insect present a striated appear-
ance, owing to alternate light and dark
bands (Fig. 1 1 1) , the former being singly
refracting, or isotropic, and the latter
doubly refracting, or anisotropic.
The minute structure of these fibers,
being extremely difficult of interpreta-
tion, has given rise to much difference of
opinion. The most plausible view is
that of van Gehuchten, Janet and others,
who hold that both kinds of dark bands
(Fig. 112) consist of highly elastic threads
of spongioplasm (anisotropic) embedded
in a matrix of clear, semi-fluid, nutritive
hyaloplasm (isotropic). The spongio-
plasmic threads of the long bands extend
longitudinally and those of the short bands {"Krause's membrane'')
radially, in respect to the form of the fiber. Moreover, the attenuated
extremities of the longitudinal fibrillae connect with the radial fibrill^,
the points of connection being marked by sHght thickenings, or nodes,
which go to make up Krause's membrane.
Fig. 112. — Minute structure of a
striated muscle fiber. A , longitudinal
section; B, transverse section in the
region of I; C, transverse section in the
region of n. I, longitudinal fibrillas;
n, Krause's membrane; nl, nucleus;
r, radial fibrillae; 5, sarcolemma. — After
Janet.
ANATOMY AND PHYSIOLOGY 79
Under nervous stimulus a muscle shortens and thickens because its
component fibers do, and this in turn is attributed to the shortening and
thickening of the longitudinal fibrillar. When the stimulus ceases, the
radial fibrillae, by their elasticity, possibly pull the longitudinal ones
back into place. The last word has not been said, however, upon this
perplexing subject.
Muscular Power. — The muscular exploits of insects appear to be
marvellous beside those of larger animals, though they are often exag-
gerated in popular writings. The weakest insects, according to Plateau,
can pull five times their own weight and the average insect, over twenty
times its weight, while Donacia (ChrysomeHdae) can pull 42.7 times its^
weight. As contrasted with these feats, a man can pull in the same
fashion but 0.86 of his weight and a horse from 0.5 to 0.83. How are
these differences explained?
It is incorrect to say that the muscles of insects are stronger than
those of vertebrates, for, as a matter of fact, the contractile force of a
vertebrate muscle is greater than that of an insect muscle, other things
being equal. The apparently greater strength of an insect in propor-
tion to its weight is accounted for in several ways. The specific gravity
of chitin is less than that of bone, though it varies greatly in both sub-
stances. Furthermore, the external skeleton permits muscular attach-
ments of the most advantageous kind as compared with the internal
skeleton, so that the muscles of insects surpass those of vertebrates as
regards leverage. These reasons are only of minor importance, how-
ever. Small animals in general appear to be stronger than larger
animals (allowing for the differences in weight) for the same reason that
a smaller insect has more conspicuous strength than a larger one, when
the two are similar in everything except weight. For example : where
a bumblebee can pull 16.1 times its own weight, a honey bee can pull
20.2; and where the same bumblebee can carry while flying a load
0.63 of its own weight, the honey bee can carry 0.78. Always, as
Plateau has shown, the lighter of two insects is the stronger in respect
to external manifestations of muscular force — in the ratio of this muscu-
lar strength to its own weight.
To understand this, let us assume that a beetle continues to grow (as
never happens, of course). As its weight is increasing so is its strength
— but not in the same proportion. For while the weight — say that of a
muscle — increases as the cube of a single dimension, the strength of the
muscle (depending solely upon the area of its cross-section) is increasing
only as the square of one dimension — its diameter. Therefore the
8o ENTOMOLOGY
increase in strength lags behind that of weight more and more; conse-
quently more and more strength is required simply to move the insect
itself, and less and less surplus strength remains for carrying additional
weight. Thus the larger insect is apparently the weaker, though
it is actually the stronger, in that its total muscular force is greater.
The writer uses this explanation to account also for the inability of
certain large beetles and other insects to use their wings, though these
organs are well developed. Increasing weight (due to a larger supply
of reserve food accumulated by the larva) has made such demands upon
the muscular power that insufhcient strength remains for the purpose of
flight.
Statements such as this are often seen — a flea can jump a meter, or
six hundred times its own length. Almost needless to say, the length of
the body is no criterion of the muscular power of an animal.
4. Nervous System
The central nervous system extends along the median line of the floor
of the body as a series of ganglia connected by nerve cords. Typically,
there is a ganglion (double in origin) for each primary segment, and the
connecting cords, or commissures, are paired; these conditions are most
nearly realized in embryos and in the most generalized insects — Thysa-
nura (Fig. 113). In all adult insects, however, the originally separate
gangha consolidate more or less (Fig. 114) and the commissures fre-
quently unite to form single cords. Thus in Tabanus (Fig. 1 14, C) the
three thoracic gangha have united into a single compound ganglion
and the abdominal ganglia are concentrated in the anterior part of the
abdomen; in the grasshopper, the nerve cord, double in the thorax, is
single in the abdomen. Various other modifications of the same nature
occur.
Cephalic Ganglia. — In the head the primitive .ganglia always unite
to form two compound ganglia, namely, the brain and the sub (esophageal
ganglion (disregarding a few anomalous cases in which the latter is said
to be absent).
The brain, or supra oesophageal ganglion (Fig. 115), is formed by the
union of three primitive ganglia, or neuromeres (Fig. 57), namely, (i)
the protocerebrum, which gives off the pair of optic nerves; (2) the deuto-
cerebrum, which innervates the antennae; and (3) the tritocerebrum,
which in Apterygota bears a pair of rudimentary appendages that are
regarded as traces of a second pair of antennae.
ANATOMY AND PHYSIOLOGY
The suboesophageal ganglion (Fig. 115) is al-
ways connected with the brain by a pair of nerve
cords {cesephageal commissures) between which
the oesophagus passes. This ompound ganglion
represents at most four neuromeres: (i) mandi-
bular, innervating the mandibles; (2) superlin-
gual, found by the author in Collembola, but not
yet reported in the less generahzed insects; (3)
maxillary, innervating the maxilte; (4) labial,
which sends a pair of nerves to the labium.
The minute structure of the brain, thgouh
highly complex, has received considerable study,
but will not be described here for the reason that
the anatomical facts are of no general interest
so long as their physiological interpretation re-
mains obscure.
Sympathetic System. — ^Lying along the
median dorsal line of the oesophagus is a recurrent,
or stomato gastric, nerve Fig. 116), which arises
anteriorly in a frontal ganglion and terminates
posteriorly in a stomachic ganglion situated at
the anterior end of the mid intestine. Con-
nected with the recurrent nerve are two pairs of
lateral gangha, the anterior of which innervate
the dorsal vessel and the posterior, the tracheae
of the head. The ventral nerve cord may include
also a median nerve thread (Fig. 113) which gives
oft" paired transverse nerves to the muscles of
the spiracles.
Structure of Ganglia and Nerves. — A gang-
lion consists of (i) a dense cortex, composed of
ganglion cells (Fig. 117), each of which has a large
rounded nucleus and gives off usually a single
nerve fiber; and (2) a clear medullary portion
(Punktsubstanz) derived from the processes of the
cortical ganglion cells and serving as the place
of origin of nerve fibrillas. There are, however,
ganglion cells from which processes may pass
directly into nerve fibrillae.
A nerve fiber, in an insect, consists of an axis-
cylinder, composed of fibrillae, and an enveloping
membrane, or sheath. The axis-cylinder is the
transmitting portion and the ganglia are the
b-W-
S"'
■sy
III
Fig. 113. — Central nerv-
ous system of a thysanu-
ran, Machilis. The
thoracic and abdominal
ganglia are numbered in
succession. a, antennal
nerve; b, brain; e, com-
pound eye; /, labial nerve;
m, mandibular nerve;- mx,
maxillary nerve; o, ceso-
phagus; ol, optic lobe; s,
suboesophageal ganglion;
sy, sympathetic nerve. —
After GuDEMANS.
82
ENTOMOLOGY
trophic centers, i. e., they regulate nutrition. A nerve is always
either sensory, transmitting impulses inward from a sense organ; or
Fig. 114. — Successive stages in the concentration of the central nervous system of Diptera.
A, Chironomus; B, Empis; C, Tabanus; D, Sarcophaga. — After Brandt.
else motor, conveying stimuli from the central nervous system outward
to muscles, glands, or other organs.
Functions." — The brain innervates the chief sensory organs (eyes and
antennae) and converts the sensory stimuli that it receives into motor
Pig. 115. — Nervous system of the head of a cockroach, a, antennal nerve; ag, anterior
lateral ganglion of sympathetic system; b, brain; d, salivary duct; /, frontal ganglion; h,
hypopharynx; I, labrum; li, labium; m, mandibular nerve; mx, maxillary nerve; nl, nerve to
labrum; nli, nerve to labium; o, optic nerve; oc, oesophageal commissure; oe, oesophagus;
pg, posterior lateral ganglion of sympathetic system; r, recurrent nerve of sympathetic
system; s, suboesophageal ganglion. — After Hofer.
stimuli, which effect co-ordinated muscular or other movements in
response to particular sensations from the environment. The brain
is the seat of the will, using the term "will" in a loose sense; it directs
locomotor movements of the legs and wings. An insect deprived of its
ANATOMY AND PHYSIOLOGY
83
brain cannot go to its food, though it is able to eat if food be placed in
contact with the end-organs of taste, as those ^^ ^
of the palpi ; furthermore, it walks or flies in an
erratic manner, indicating a lack of co-ordina-
tion of muscular action.
The suboesophageal ganglion controls the
mouth parts, co-ordinating their movements as
well as some of the bodily movements.
The thoracic ganglia govern the appendages
of their respective segments. These ganglia
and those of the abdomen are to a great extent
independent of brain control, each of these
ganglia being an individual motor center for
its particular segment. Thus decapitated in-
sects are still able to breathe, walk or fly, and
often retain for several days some power of
movement.
In regard to the sympathetic system, it
has been shown experimentally that the fron-
tal ganglion controls the swallowing movements
and exerts through the stomatogastric nerve
a regulative action upon digestion. The dor-
sal sympathetic system controls the dorsal
vessel and the salivary glands, while the
ventral sympathetic system is concerned with
the spiracular muscles.
5. Sense Organs
For the reception of sensory impressions
from the external world, the armor-Hke integu-
ment of insects is modified in a great variety of ways. Though sense
Fig. 116.— Sympathetic nerv-
ous system of an insect,
diagrammatically represented.
a, antennal nerve; b, brain; /,■
frontal ganglion; I, I, paired
lateral ganglia; m, nerves to
upper mouth parts; o, op-
tic nerve; r, recurrent
nerve; 5, nerve to saUvary
glands; st, stomachic ganglion.
— After KoLBE.
Fig. 117.— Transverse section of an abdominal gangUon of a caterpillar. /, nerve fibers; g,
gangUon cells; w, nerve sheath; p, Punktsubstanz.
84 ENTOMOLOGY
organs of one kind or another may occur on almost any part of an
insect, they are most numerous and varied upon the head and its appen-
dages, particularly the antennae.
Anteimal Sensilla. — Some idea of the diversity of form in antennal
sense organs may be obtained from Figs. 1 18-127, taken from a paper
by Schenk, whose useful classification of antennal sensilla, or sense
organs, is here outlined:
1. Sensillum cceloconicum — a conical or peg-like projection immersed
in a pit (Figs. 118, 119). In all probability olfactory.
2. S. hasiconicum — a cone projecting above the general surface (Fig.
120). Probably olfactory.
3. S. styloconicum — a terminal tooth or peg seated upon a more or
less conical base (Fig. 121). Olfactory.
4. S. chaticum — a bristle-like sense organ (Fig. 122). Tactile.
5. S. trichodeum — a hair-hke sense organ (Figs. 123, 124). Tactile.
6. S. placodeum — a membranous plate, its outer surface continuous
with the general integument (Fig. 125). Function doubtful; not audi-
tory and probably not olfactory, though the function is doubtless a
mechanical one; Schenk suggests that this organ is affected by air
pressure, as when a bee or wasp is moving about in a confined space.
7. S. ampullaceum — a more or less flask-shaped cavity with an
axial rod (Figs. 126, 127). Probably auditory.
These types of sensilla will be referred to in physiological order.
Touch.^The tactile sense is highly developed in insects, and end-
organs of touch, unlike those of other senses, are commonly distributed
over the entire integument, though the antennae, palpi and cerci are
especially sensitive to tactile impressions.
The end-organs of touch are bristles (sensilla chastica) or hairs
(sensilla trichodea), each arising from a special hypodermis ceU and
having connection with a nerve. SensiUa chsetica doubtless receive
impressions from foreign bodies, while sensilla trichodea, being best
developed in the swiftest flying insects and least so in the sedentary
forms, may be affected by the resistance of the air, when the insect or
the air itself is in motion.
Not all the hairs of an insect are sensory, however, for many of them
have no nerve connections.
In blind cave insects the antennae are very long and are exquisitely
sensitive to tactile impressions.
Taste. — The gustatory sense is unquestionably present in insects, as
is shown both, by common observation and by precise experimentation.
ANATOMY AND PHYSIOLOGY
85
Will fed wasps with sugar and then replaced it with powdered alum,
which the wasps unsuspectingly tried but soon rejected, cleaning the
tongue with the fore feet in a comical manner and manifesting other
Figs, i 18-12 7. — Types of antennal sensilla, in longitudinal section (excepting Figs. 121
and 122). Fig. 118, sensillum coeloconicum ; 119, coeloconiciim; 120, basiconicum; 121,
styloconicum; 122, chaeticum; 123, trichodeum; 124, trichodeum; 125, placodeum; 126,
ampuUaceum; 127, ampullaceum; c, cuticula; h, hypodermis; n, nerve; 5. sensory cell.
Figs. 118, 120, 123, 125, 126, honey bee, Apis mellifera; 119, 121, 124, Fidonia piniaria;
122, moth, Ino pruni; 127 wasp, Vespa crabro. — After Schenk.
signs of what we may call disgust. Forel offered ants honey mixed with
morphine or strychnine; the ants began to feed but at once rejected the
mixture. In its range, however, the gustatory sense of insects differs
often from that of man. Thus Will found that Hymenoptera refused
86 ENTOMOLOGY
honey with which a very httle glycerine had been mixed (though Musci-
dse did not object to the glycerine) and Forel found that ants ate un-
suspectingly a mixture of honey and phosphorus until some of them
were killed by it. Under the same circumstances, man would be able
to detect the phosphorus but not the glycerine.
Location of Gustatory Organs. — As would be expected, the end-
organs of taste are situated near the mouth, commonly on the hypo-
pharynx (Fig. 128), epipharynx and maxillary palpi. On the tongue of
the honey bee the taste organs appear externally as short setae (Fig. 129)
and on the maxillae of a wasp as pits, each with a cone, or peg, project-
ing from its base (Figs. 130, 131). Similar taste pits and pegs were
Pig. 128. — -Section through tongue of wasp, Vespa vul- Fig. 129. — Tongue of honey
garis. c, cuticula; g, gland cell; h, hypodermis; «, nerve; hee, Apis mellifera. /», protect-
ob, gustatory bristle; ph, protecting hair; sc, sensory cell; ing bristles; s, terminal spoon;
tb, tactile bristle. — After Will. /, taste setae. — After "Will.
found by Packard on the epipharynx in most of the mandibulate orders
of insects.
Histology. — The end-organs of taste arise from special hypodermis
cells, as minute setae or, more commonly, pegs, each seated in a pit, or
cup, and connected with a nerve fiber (Figs. 131, 132). In some cases,
however, it is difficult to decide whether a given organ is gustatory or
olfactory, owing to the similarity between these two kinds of structures.
In aquatic insects, indeed, the senses of taste and smell are not differen-
tiated, these forms having with other of the lower animals simply a
"chemical" sense.
Smell. — In most insects the sense of smell is highly efficient and in
many species it is inconceivably acute. Hosts of insects depend chiefly
on their olfactory powers to find food, for example many beetles, the
flesh flies and the flower-visiting moths; or else to discover the opposite
ANATOMY AND PHYSIOLOGY
87
sex, as is notably the case in saturniid moths. In dragon flies, however,
this sense is reHed upon far less than that of sight.
Organs of Smell.^By means of simple but conclusive experiments,
Hauser and others have shown that the antennae are frequently olfactory
— though not to the exclusion of tactile or auditory functions, of course.
Hauser found that ants, wasps, various flies, moths, beetles and larvae,
which react violently toward the vapor of turpfentine, acetic acid and
other pungent fluids, no longer respond to the same stimuli after their
antennae have been amputated or else covered with paraffine to exclude
the air. His experiments were con-
ducted under conditions such that the
results could not be ascribed to the shock
of the operation or to effects upon the
gustatory or respiratory systems; except
for having lost the sense of smell, the
insects experimented upon behaved in
, _ __ a normal manner. It should be said,
Fig. 130. — Under side of left maxilla
of wasp, Vespa vulgaris, p, palpus;
pr, protecting hairs; tc, taste cup; th,
tactile hair. — After Will.
Fig. 131. — Longitudinal section of gustatory
end-organ (tc, of Pig. 130). c, cuticula; k, hypo-
dermis; sc, sensory cell; tc, taste cup. — After
Will.
however, that Carabus, Melolontha and Silpha still reacted to some
extent toward strong vapors even after the extirpation of the antennae;
while in Hemiptera the loss of the antennae did not lessen the response
to the odors used. These facts indicate that the sense of smell is not
always confined to the antennae; indeed the maxillary palpi are frequently
olfactory, as in Silpha and Hydaticus; also the cerci, as in the cock-
roach and other Orthoptera. Experiments indicate that an insect per-
ceives some odors by means of the antennae and others by the palpi
or other organs. Hauser found that the flies Sarcophaga and Calli-
phora, after the amputation of their antennae, became quite indifferent
toward decayed meat, to which they had previously swarmed with
88 ENTOMOLOGY
great persistence, though their actions in all other respects remained
normal. Males of many moths and a few beetles are unable to find
the females (see beyond) when the former are deprived of the use of
their antennae.
Fig. 132. — Taste cup from maxilla of
Bombus. sc, sensory cell; n, nerve. — After
Will.
Fig. 133. — Section of antennal olfactory
organ of grasshopper, Caloptenus. c, cutic-
ula; m, membrane; n, nucleus of sensory
cell; nv, nerve; p, pit with olfactory peg,
pg, pigment. — After Hauser.
End-Organs. — Structures which are . regarded as olfactory end-
organs occur commonly on the antennae, often on the maxillary and
labial palpi and sometimes on the cerci. These end-organs are hypo-
dermal in origin and consist, generally speaking, of a multinucleate
cell (Fig. 133) penetrated by a nerve and prolonged into a chitinous
bristle or peg, which is more or less enclosed in a pit, as in Tahanus
(Fig. 134). In many instances, however, the end-organs take the
form of teeth or cones projecting from the general surface of the antenna,
as in Vespa (Fig. 135). These cones are usually less numerous than
the pits; in Vespa crahro, for example, the teeth number 700 and the
pits from 13,000 to 14,000 on each antenna. The pits are even more
numerous in some other insects; thus there are as many as 17,000 on
each antenna of a blow fly (Hicks). The male of Melolontha vulgaris,
which seeks out the female by the sense of smell, has according to
Hauser 39,000 pits on each antenna, and the female only 35,000. Pits
presumably olfactory in function have been found by Packard on the
maxillary and labial palpi of Perla and on the cerci of the cockroach,
Periplaneta atnericana. Vom Rath has described four kinds of sense
ANATOMY AND PHYSIOLOGY
89
hairs from the two larger of the four caudal appendages of a cricket,
Gryllus; some of these (Fig. 136) may be olfactory, though possibly
tactile. The same author found on the terminal palpal segment in
various Lepidoptera a large flask-shaped invagination (Fig. 137) into
which project numerous chitinous rods, each a process of a sensory
cell, which is supplied by a branch of the principal palpal nerve; these
peculiar organs are inferred to be olfactory.
The chief reason for regarding these various end-organs as olfactory
is that they appear from their structure to be better adapted to receive
that kind of an impression than any
other, so far as we can judge from our
own experience. Though it is easy to
demonstrate that the antennae, for ex-
ample, are olfactory, it frequently hap-
FiG. 134. — Section through antennal olfactory
pit of fly, Tabanus. c, cuticula; p, pit with peg;
pb, protecting bristles; s, sensory cell. — After
Hauser.
Fig. 135. — Longitudinal section of
antennal olfactory organ of wasp,
Vespa. c, olfactory cell; en, olfactory
cone; ct, cuticula; h, hypodermis cells;
n, nerve; r, rod. — After Hauser.
pens that the antennae bear several distinct forms of sensory end-organs, so
minute and intermingled that their physiological differences can scarcely
be ascertained by experiment but must be inferred from their peculiarities
of structure. Schenk, however, has arrived at precise results by compar-
ing the an.tennal sensilla in the two sexes, selecting species in which the
antennae exhibit a pronounced sexual dimorphism, in correlation with sex-
ual differences of behavior. Taking Notolophus aniiqua, in which the
male seeks out the female by means of antennal organs of smell, he
finds that the male has on each antenna about 600 sensilla cceloconica
and the female only 75; similarly in the geometrid Fidonia, in which
the ratio is 350 to 100. The sensilla styloconica also, of these two
genera, are regarded as olfactory organs. These two kinds of end-
90
ENTOMOLOGY
organs are not only structurally adapted for the reception of olfactory
stimuli, but their numerical differences accord with the observed differ-
ences in the olfactory powers of the two sexes, there being no other
antennal end-organs to enter into the consideration.
Dr. N. E. Mclndoo has denied that the antennae are olfactory
organs. He finds, in all the large orders of insects, and on almost all
parts of the body and legs, on the bases of the wings, and in other situa-
tions, the structures that he terms olfactory pores, to which he has
devoted an immense amount of study.
Assembling. — It is a fact, well known to entomologists, that the
females of many moths and some beetles are able by emitting an odor to
Fig. 136. — Longitudinal section of a por-
tion of a caudal appendage of a cricket,
Gryllus domeslicus. b, bladderlike hair; c,
cuticula; h, hypodermis; n, nerve; ns, non-
sensory setae; sc, sense cell; sh, sensory hair.
— After VOM Rath.
Fig. 137. — Longitudinal section of apex
of palpus of Pier is. c, cuticula; h, hypo-
dermis; «, nerve; s, scales; 5C, sense cells. —
After VOM Rath.
attract the opposite sex, often in considerable numbers. Under favor-
able conditions, a freshly emerged female of the promethea moth, exposed
out of doors in the latter part of the afternoon, will attract scores of the
males. A breeze is essential and the males come up against the wind;
if they pass the female, they turn back and try again until she is located,
vibrating the antennas rapidly as they near her. The female, mean-
while, exhales an appreciable odor, chiefly from the region of the ovi-
positor, and males will congregate on the ground at a spot where a
female has been. If one of these males is deprived of the use of his
antennae, however, he flutters about in an aimless way and is no longer
able to find the female.
Among beetles, males of Polyphylla gather and scratch at places
ANATOMY AND PHYSIOLOGY 9 1
where females are about to emerge from the ground. Prionus also
assembles, as Mrs. Dimmock observed in Massachusetts. In this
instance many males, with palpitating antennae, ran and flew to the
female; moreover, a number oi females were attracted to the scene.
Sounds of Insects. — Before considering the sense of hearing, some
account of the sounds of insects is desirable. Most of these are made by
the vibrations of a membrane or by the friction of one part against
another.
The wings of many Diptera and Hymenoptera vibrate with sufficient
speed and regularity to give a definite note. The wing tone of a honey
bee is A' and that of a common house fly is F'. From the pitch the
number of vibrations may be determined; thus ^' means 440^ vibrations
per second and F', 352. The numbers thus ascertained may be verified
by Marey's graphic method (Fig. 76) ; he found that the fly referred to
actually made 330 strokes per second against the smoked surface of a
revolving cylinder.
Flies, bees, dragon flies and some beetles make buzzing or humming
sounds by means of the spiracles, there being behind each spiracle a
membrane or chitinous projection which vibrates during respiration.
This "voice" should be distinguished from the wing tone when both
are present, as in bees and flies. A fly will buzz when held by the
wings, and some gnats continue to buzz after losing wings, legs and
head. The wing tone is the more constant of the two; in the honey bee
it is ^', falling to E' if the insect is tired, while the spiracular tone of the
same insect is at least an octave higher {A") and often rises to B" or
C", according to the state of the nervous system; in fact, it is possible
and even probable that various spiracular tones express different
emotions, as is indicated by the effects produced by the voice of the old
queen bee upon the young queens and the males.
The well-known ''shrilling" of the male cicada is produced by the
rapid vibration of a pair of membranes, or drums, situated on the basal
abdominal segment, and vibrated each by means of a special muscle.
Frictional sounds are made by beetles in a great variety of ways : by
the rubbing of the pronotum against the mesonotum (many Cerambyci-
dae) ; or of abdominal ridges against elytral rasps {Elaphrus, Cychrus) ;
or two dorsal abdominal rasps against specialized portions of the wing
folds (Passalus cornutus), not to mention other methods. In most cases
one part forms a rasp and the other a scraper, for the production of
sound.
^ Upon the basis of C as 264 vibrations per second. The C of the physicist has 256 as
its frequency of vibration.
92 ENTOMOLOGY
In many of these instances the sound serves to bring the two sexes
together and is not necessarily confined to one sex; thus in Passalus cor-
nutus both sexes stridulate, and the larva as well.
A few moths (Sphingidae) and a few butterflies make sounds; the
South American butterfly Ageronia feronia emits a sharp crackling
noise as it flies. A rasp and a scraper have been found in several ants,
though ants very seldom make any sounds that can be distinguished
by the human ear; Mutilla, however, makes a distinct squeaking sound
by means of a stridulating organ similar to those of ants.
Stridulating organs attain their best development in Orthoptera, in
which group the abihty to stridulate is often restricted to the male,
though not so often as is commonly supposed. Among Locustidae,
Stenohothrus rubs the hind femora against the tegmina to make a
sound, the femur bearing a series of teeth, which scrape across the
elevated veins of the wing-cover; while the male of Dissosteira makes a
crackling sound during flight or while poising, by means of friction
between the front and hind wings, where the two overlap.
Tettigoniidae and Gryllidae stridulate by rubbing the bases of the teg-
mina against each other. Thus in the male Microcentrum laurifolium
the left tegmen, which overlaps the right, bears a file-like organ of about
fifty-five teeth (Fig. 138), while the opposite tegmen bears a scraper, at
right angles to the file. The tegmina are first spread a little; then, as
they close gradually, the scraper clicks across the teeth, making from
twenty to thirty sharp "tic"- like sounds in rapid succession. This
call guides the female to the male and when they are a few inches apart
she makes now and then a short, soft chirp, to which he responds with a
similar chirp, which is quite unlike the first call and, moreover, is
made by the opening of the tegmina. These and other details of the
courtship may readily be observed in twilight and even under artificial
light, as the latter, if not too strong, does not disturb the pair. Some-
thing similar may be observed in the daytime in Orchelimum, Xiphidium
and the tree crickets, (Ecanthus. The stridulating areas are usually
membranous and. the rasping organs are modified veins. Frequently
the wing-covers bulge out to form a resonant chamber that reinforces
the sound, as in the katydid.
The naturalist can recognize many a species of grasshopper by its
song; Scudder has expressed some of these songs in musical notation.
The usual song of the common meadow-grasshopper, Orchelimum vul-
gare, may be represented by a prolonged zr . . . sound, followed by
a staccato jip-jip-jip-jip. . . .
ANATOMY AND PHYSIOLOGY
93
In Orthoptera, the frequency of stridulation increases with the tem-
perature; and the correlation between the two is so close that it is easy
Fig. 138. — Stridulating organs of Microcentrum laurifolium. A, dorsal aspect of
file (st) when the tegmina are closed; B, ventral aspect of left tegmen to show file; C, dorsal
aspect of right tegmen to show scraper (s).
to compute the temperature from the number of calls per minute, by
means of formulae. The formula for a common cricket [probably a
tree-cricket, CEcanthus niveus], as given by Professor Dolbear, is
r = 50 H , which simplified is T = 40 H
4 4
Here T stands for temperature and N, the rate per minute.
A similar formula for the katydid {Cyrtophyllus perspicillatus) ,
based upon observations made by R. Hayward, would be
r = 60 +
N- ig
Here, in computing N, either the "katy-did" or the "she-did" is taken
as a single call.
94 ENTOMOLOGY
Professor A. F. Shull, who has made precise observations on the
stridulation of (Ecanthus, finds that there are numerous variations of.
rate that cannot be accounted for by differences of temperature; that
Dolbear's formula cannot be appHed without a possible error of 6.65°
F.; that humidity seems to affect the rate of chirping and that crickets
show a certain individuality in their manner of chirping under the same
external conditions.
Hearing. — There is no doubt that insects can hear. The presence
of sound-making organs is strong presumptive evidence that the sense of
hearing is present. Female grasshoppers and beetles make locomotor
and other responses to the sounds of the males, and male grasshoppers
will answer the counterfeit chirping made with a quill and a file.
Auditory organs are not restricted to any one region of an insect, but
occur,. according to the species, on antennae, abdomen, legs, or elsewhere.
The antennae of some insects are evidently stimulated by certain
notes, particularly those made by their own kind. Thus the antennae
of the male mosquito are auditory, as proved by the well-known experi-
ments of Mayer. He fastened a male Culex to a microscope slide and
sounded various tuning forks. Certain tones caused certain of the
antennal hairs to vibrate sympathetically, and the greatest amount of
vibration occurred in response to 512 vibrations per second, or the note
C", which is approximately the note upon which the female hums.
The male probably turns his head until the two antennae are equally
affected by the note of the female, when, by going straight ahead, he is
able to locate her with great precision.
In the lack of experimental evidence, other organs are inferred to be
auditory on account of their structure. Locustidae bear on each side of
the first abdominal segment a tympanal sense organ — the subject of
Graber's well-known figure (Fig. 139) . This organ is admirably adapted
to receive and transmit sound-waves. The tympanum, or membrane,
is tense, and can vibrate freely, as the air pressure against the two sur-
faces of the membrane is equalized by means of an adjacent spiracle,
which admits air to the inner surface. Resting against the inner face
of the tympanum are two processes (Fig. 139, p, p), which serve proba-
bly to transfer the vibrations, and there is also a delicate vesicle con-
nected by means of an intervening ganglion with the auditory nerve,
which in this case comes from the metathoracic ganghon. The nerve
terminations consist of delicate bristle-like processes which are probably
affected by the oscillations of the fluid contained in the vesicle just
referred to.
ANATOMY AND PHYSIOLOGY
95
Other tympanal organs, doubtless auditory, are found on the fore
tibiae of Tettigoniidas, ants, termites and PerHda), on the femora of Pedicu-
hdae and the tarsi of some Coleoptera.
Several types of diordotonal organs have been described, of which
those of the transparent Core/Ara larva may serve as an example. These
organs, situated on each side of abdominal segments 4-10, inclusive,
consist each (Fig. 140) of a tense cord, probably capable of vibration,
which is attached at its posterior end to the integument and at its
-i^
Fig. 139. — Inner aspect of right tympanal sense
organ of a grasshopper, Caloplenus italicus. b. chitin-
ous border; c, closing muscle of spiracle; gn, gan-
glion; m, tympanum; n, nerve; o, opening muscle
of spiracle; p, p, processes resting against tympan-
um; s, spiracle; tm, tensor muscle of tympanum; v,
vesicle. After Graber.
Fig. 140. — Chordotonal sense
organ of aquatic dipterous larva,
Corethra plumicornis. cd, cord; eg,
chordotonal ganglion; /, fibers of an
, integumental nerve; g, ganglion of
ventral chain; I, ligament; m, lon-
gitudinal mujcles; n, chordotonal
nerve; r, rods (nerve terminations);
t, tactile setae. — After Graber.
anterior end to a ligament. Between the cord and the supporting
ligament is a small ganglion, which receives a nerve from the principal
ganglion of the segment.
Vision. — The external characters of the two kinds of eyes — ocelli and
compound eyes — have already been described. While the lateral ocelli
are comparatively simple in structure, consisting of a small number of
cells, the dorsal ocelli almost rival the compound eyes in complexity.
Dorsal Ocelli. — These consist (Fig. 141) of (i) lens, (2) vitreous
body, (3) retina, (4) nerve fibers, (5) pigmented hypodermis cells, and (6)
96
ENTOMOLOGY
accessory cells, between the retinal cells and the nerve fibers. The lens,
usually biconvex in form, is a local thickening of the general cuticula;
it is supplemented in its function by the vitreous body, consisting of a
layer of transparent hypodermis cells; these in many insects are elon-
gate, constituting a vitreous layer of rather more importance than the
one represented in Fig. 141. The retina consists
of cells more or less spindle-shaped and associated
in pairs or in groups of two or three, each group
being termed a retinula. The basal end of each
retinal cell is continuous with a nerve fiber (Fig.
142), according to Redikorzew and others, and in
Fig. 141. — Median ocellus of honey bee, Apis mellifera, in
sagittal section, h, hypodermis; /, lens; n, nerve; p, iris pigment;
r, retinal cells; v, vitreous body. — After Redikorzew.
— n
Fig. 142. — An ocel-
lar retinula of the honey
bee, composed of two
retinal cells. A, longi-
tudinal section; B,
transverse section; n,
n, nerves; p, pigment;
r, rhabdom.- After Red-
ikorzew.
some instances (Calopteryx) a nerve fiber enters
the cell. Each retinula contains a longitudinal
rod, or rhabdom, in the secretion of which all the
cells of the retinula are concerned. Between the
retinal cells and nerve fibers are indifferent, or accessory cells. Pig-
ment granules, usually black, are contained in these cells, also in
the retinal cells and around the lens, in the last instance forming the
iris.
Vision by Ocelli.— Though the ocellus is constructed on somewhat
the same plan as the human eye, its capacity for forming images must
ANATOMY AND PHYSIOLOGY
97
be extremely limited; for since the form of the lens is fixed and also the
distance between the lens and the retina, there is no power of accom-
modation, and most external objects are out of focus; to make an
image, then, the object must be at one definite distance from the lens,
and as the lens is usually strongly convex, this distance must be small;
in other words, insects, like spiders, are very near-sighted, so far as the
oceUi are concerned; furthermore, the small number of retinal rods
implies an image of only the coarsest kind.
If the compound eyes of a grasshopper are covered with an opaque
varnish and the insect is placed in a box with only a single opening, it
readily finds its way out by means of its ocelli; if the three ocelli also
are covered, however, it no longer does so,
except by accident, though it can make its
escape when only one of the ocelli is left
uncovered. The ocelli, then, can distinguish
light from darkness — and they are probably
more serviceable to the insect in this way
than in forming images.
Compound Eyes. — As regards delicacy and
intricacy of structure, the compound eye of
an insect is scarcely if at all inferior to the eye
of a vertebrate. In radial section (Fig. 143),
a compound eye appears as an aggregation
of] similar elongate elements, or ommaiidia,
each of which ends externally in a facet. The ^'"y ^43.-Portion of com-
•' pound eye of fly, Calltphora
following structures compose, or are concerned vomitoria, radial section, c, cor-
.,1 1 ,.j. / \ / \ nea; i, iris pigment; n, nerve
With, each OmmatldlUm: (l) cornea, (2) Crys- fibers; nc, nerve cells; r. retinal
talline lens, or cone, (t,) rhabdom and retinula, pigment; t, trachea.— After
/ \ • /• • 1 • 7\ / \ r HiCKSON.
(4) pigment {ins and rehnal), (5) jenestrate
membrane, (6) fibers of the optic nerve, (7) trache<B.
The cornea (Fig. 144) is a biconvex transparent portion of the exter-
nal chitinous cuticula. Immediately beneath it are the cone cells, which
may contain a clear fluid or else, as in most insects, solid transparent
cones. The rhabdom is a transparent chitinous rod or a group of rods
(rhabdomeres) situated in the long axis of the ommatidium and sur-
rounded by greatly elongated cells, which constitute the retinula.
Two zones of pigment are present: an outer zone, of iris pigment, in
which the pigment in the form of fine black granules is contained
chiefly in short cells that surround the retinula distally; and an inner
zone, of retinal pigment, in which the pigment cells are long and slender,
7
98
ENTOMOLOGY
and enclose the retinula proximally. All these
parts are hypodermal in origin, as is also the
fenestrate basement membrane, through which
pass tracheae and nerve fibers. The nerve
fibrillae, which are ultimate branches of the
optic nerve, pass into the retinal cells — the
end-organs of vision. Under the basement
membrane is a fibrous optic tract of com-
plex structure.
Compound eyes are of three types: (i)
eucone, in which the cone-cells form solid crys-
talhne cones; (2) pseudocone, in which the cone-
cells contain a transparent fluid; and (3) acone,
in which there are no cones, though the cone-
cells are present.
Physiology. — After much experimentation
and discussion upon the physiology of the com-
pound eye — the subject of the monumental
works of Grenacher and Exner — Miiller's
"mosaic" theory is still generally accepted,
though it was proposed early in the last cen-
tury. It is thought that an image is formed
by thousands of separate points of light, each
of which corresponds to a distinct field of
vision in the external world. Each ommati-
dium is adapted to transmit light along its axis
only (Fig. 145), as oblique rays are lost by
absorption in the black pigment which sur-
rounds the crystalline cone and the axial
rhabdom. Along the rhabdom, then, light can
reach and affect the terminations of the optic
nerve. Each ommatidium does not itself form
a picture ; it simply preserves the intensity and
nucleus; nv, nerve fibrillae; r ^ ^^ t r • i
PC pseudocone; pg\ pg\ cells color of the fight from ouc particular portion
containing iris pigment; pg\ f ^^ ^^^ f ^-g-^j^ and whcu this is doue by
cell containing retinal pigment ; ' •'
r, one of the six retinal cells hundreds or thousands of contiguous ommati-
which compose the retinula; Wj, ,. . ,. ah ^i j_ ,i ■ /
rhabdom. composed of six rhab- dia, an image results. All that the painter
domeres;!. trachea; <ir. tracheal ^J^gg ^J^q copieS an object, is tO put together
vesicle. — After Hickson. ' . ^ . •' ' ^ °
patches of light in the same relations of qual-
ity and position that he finds in the object itself — and this is essen-
PiG. 144. — Structure of an
ommatidium of Calliphora
vomiloria. A, radial section
(chiefly); B, transverse sec-
tion through middle region;
C, transverse section through
basal region; hm, basement
membrane; c, cornea; n,
ANATOMY AND PHYSIOLOGY
99
tially what the compound eye does, so far as can be inferred from its
structure.
Exner, removing the cones with the corneal cuticula (in Lampyris),
looked through them from behind with the aid of a microscope and
found that the images made by the separate ommatidia were either
very close together or else overlapped one another, and that in the
latter case the details corresponded; in other words, as many as twenty
or thirty ommatidia may co-operate to form an image of the same por-
tion of the field of vision; this "superposition"
image being correspondingly bright — an advan-
tage, probably, in the case of nocturnal insects.
Large convex eyes indicate a wide field of
xdsion, while small numerous facets mean dis-
tinctness of vision, as Lubbock pointed out. The
closer the object the better the sight, for the
greater will be the number of lenses employed
to produce the impression, as Mollock says.
If Miiller's theory is true, an image may be
formed of an object at any reasonable distance,
no power of accommodation being necessary ;
while if, on the other hand, each cornea with
its crystalHne cones had to form an image after
the manner of an ordinary hand-lens, only objects f'^; i4S-— Diagram of
-' _ J ■ J J outer transparent portion of
at a definite distance could be imaged. an ommatidiiun to illustrate
The limit of the perception of form by insects ^ay T^fTnTthf repeated
is placed at about two meters for Law^ym, i.^o reflection and absorption of
./ an oblique ray (5), which at
meters for Lepidoptera, 68 centimeters for length emerges at c. p, iris
Diptera and 58 centimeters for Hymenoptera. p^^^^^*-
It is generally agreed, however, that the compound eyes are specially
adapted to perceive movements of objects. The sensitiveness of insects
to even sHght movements is a matter of common observation; often,
however, these insects can be picked up with the fingers, if the operation
is performed slowly until the insect is within the grasp. A moving object
affects different facets in succession, without necessitating any turning
of the eyes or the head, as in vertebrates. Furthermore, on the same
principle, the compound eyes are serviceable for the perception of form
when the insect itself is moving rapidly.
The arrangement of the pigment depends adaptively upon the
quality of the light, as Stefanowska and Exner have shown; thus, when
the light is too strong, the iris and retinal pigment cells elongate around
lOO ENTOMOLOGY
the ommatidium and their pigment granules absorb from the cone
cells and rhabdom the excess of light. If the light is weak, they shorten,
and absorb but a minimum amount of light. In diurnal insects the
pigment is adapted to absorb an excess of light; in nocturnal insects,
on the contrary, it is adapted to permit a maximum amount of light
to reach the retinal cells.
Origin of Compound Eye.- — The compound eye is often said to
represent a group of ocelli, chiefly for the reason that externally there
appears to be a transition from simple eyes, through agglomerate eyes,
to the facetted type. This plausible view, however, is probably incor-
rect, for these reasons among others. In the ocellus, a single lens serves
for all the retinulae, while in the compound eye there are as many lenses
as there are retinulae. Moreover, ocelli do not pass directly into com-
pound eyes, but disappear, and the latter arise independently of the
former.
Probably, as Grenacher holds, both the ocellus and the compound
eye are derived from a common and simpler type of eye — are ''sisters,"
so to speak, derived from the same parentage.
Perception of Light through the Integument. — In various insects,
as also in earthworms, blind chilopods and some other animals, light
affects the nervous system through the general integument. Thus
eyeless dipterous larvae avoid the light, or, more precisely, they retreat
from the rays of shorter wave-length (as the blue), but come to rest in
the rays of longer wave-length (red), as if they were in darkness (see
page 307). The blind cave-beetles of the genus Anophthalmus react to
the light of a candle (Packard). Graber found that a cockroach de-
prived of its eyesight could stiU perceive light, but Lubbock found that
an ant whose eyes had been covered with an opaque varnish became
indifferent to light.
Color Sense. — Insects undoubtedly distinguish certain colors,
though their color sense differs in range from our own. Thus ants avoid
violet light as they do sunlight, but probably cannot distinguish red or
orange light from darkness; on the other hand, they are extremely
sensitive to the ultra-violet rays. Honey bees frequently select blue
flowers: white butterflies (Pieris) prefer white flowers, and yellow
butterflies (Colias) appear to alight on yellow flowers in preference to
white ones (Packard) . In fact, the color sense is largely relied upon by
insects to find particular flowers and by butterflies to a large extent to
find their mates. To be sure, insects will visit flowers after the brightly
colored petals have been removed or concealed, as Plateau found, but
ANATOMY AND PHYSIOLOGY lOI
this does not prove that the colors are of no assistance to the insect,
though it does show that they are not the sole attraction — the odor also
being an important guide. The honey bee is able to distinguish color
patterns, according to the experiments of C. H. Turner.
Problematical Sense Organs. — As all our ideas in regard to the
sensations of insects are necessarily inferences from our own sensory ex-
periences, they are inevitably inadequate. While it is certain that in-
sects have at least the senses of touch, taste, smell, hearing and sight, it
is also certain that these senses of theirs differ remarkably in range from
our own, as we have shown. We can form no accurate conception of
these ordinary senses in insects, to say nothing of others that insects
have, some of which are probably peculiar to insects. Thus they have
many curious integumentary organs which from their structure and
nerve connections are inferred to be sensory end-organs, though their
functions are either doubtful or unknown. Such an organ is the sensil-
lum placodeum (p. 84), the use of which is very doubtful, though the
organ is possibly affected by air pressure. Insects are extremely sensi-
tive to variations of wind, temperature, moisture and atmospheric
pressure, and very likely have special end-organs for the perception of
these variations; indeed, the sensilla trichodea are probably afifected
by the wind, as we have said.
The halteres of Diptera, representing the hind wings, contain sensory
organs of some sort. They have been variously regarded as olfactory
(Lee), auditory (Graber), and as organs of equilibration. When one or
both halteres are removed, the fly can no longer maintain its equilibrium
in the air, and Weinland holds that the direction of flight is affected by
the movements of these "balancers."
6. Digestive System
The alimentary tract in its simplest form is to be seen in Thysanura,
Collembola and most larvae, in which (Fig. 146) it is a simple tube ex-
FiG. 146. — Alimentary tract of a collembolan, Orchesella. F, fore gut; H, hind gut; M,
mid gut; c, cardiac valve; cm, circular muscle; Im, longitudinal muscle; p, pharynx; py,
pyloric valve.
I02 ENTOMOLOGY
tending along the axis of the body and consisting of three regions,
namely, fore, mid and hind gut. These regional distinctions are funda-
mental, as the embryology shows, for the middle region is entodermal
in origin and the two others are ectodermal, as appears beyond.
There are many departures from this primitive condition, and the
most specialized insects exhibit the following modifications (Figs. 147,
148) of the three primary regions :
Fore intestine {stomodceum) : mouth, pharynx, oesophagus, crop, pro-
ventriculus (gizzard), cardiac valve.
Mid intestine (mesenteron) : ventriculus (stomach) .
Etind intestine (proctodceum) : pyloric valve, ileum, colon, rectum,
anus.
Stomodaeuni. — The mouth, the anterior opening of the food canal,
is to be distinguished from the pharynx, a dilatation for the reception of
Fig. 147. — Alimentary tract of a grasshopper, Melanoplus differentialis. c, colon; cr,
crop; gc, gc, gastric caeca; i, ileum; m, mid intestine, or stomach; mt, Malpighian, or kidney,
tubes; o, oesophagus; p, pharynx; r, rectum; s, salivary gland of left side.
food. In the pharynx of mandibulate insects the food is acted upon by
the saliva; in suctorial forms the pharynx acts as a pumping organ, in
the mannei" already described.
The oesophagus is commonly a simple tube of small and uniform
caliber, varying greatly in length according to the kind of insect. Pass-
ing between the commissures that connect the brain with the suboeso-
phageal gangKon (Fig. 115), the oesophagus leads gradually or else
abruptly into the crop or gizzard, or when these are absent, directly
into the stomach. In addition to its function of conducting food,
the oesophagus is sometimes glandular, as in the grasshopper, in which
it is said to secrete the "molasses" which these insects emit.
The crop is conspicuous in most Orthoptera (Fig. 147) and Cole-
optera (Fig. 148) as a simple dilatation. In Neuroptera (Fig. 149) its
capacity is increased by means of a lateral pocket — the food reservoir;
this in Lepidoptera, Hymenoptera and Diptera is a sac (Fig. 150, c)
communicating with the oesophagus by means of a short neck or a
ANATOMY AND PHYSIOLOGY
103
long tube, and serving as a temporary receptacle for food. In herbiv-
orous insects the crop contains glucose formed from starch by the
action of saliva or by the secretion of the crop itself; in carnivorous
insects this secretion converts albuminoids into assimilable peptone-
like substances.
Next comes the enlargement
known as the proventriculus, or
gizzard, which is present in many
insects, especially Orthoptera and
Coleoptera (Fig. 148), and is
usually found in such mandibulate
insects as feed upon hard sub-
stances. The proventriculus is
Fig. 148. — Digestive system of a beetle,
Carabus. a, anal gland; c (of fore gut), crop;
c (of hind gut), colon, merging into rectum;
d, evacuating duct of anal gland; g, gastric
caeca; i, ileum; m, mid intestine; mt, Mal-
pighian tubes; o, oesophagus; p, proventricu-
lus; r, reservoir. — After Kolbe.
Pig. 149. — Digestive system of Myrme-
leon larva, c, caecum; cr, crop; m, mid
intestine; mt, Malpighian tubes; s, spin-
neret.— After Meinert.
lined with chitinous teeth or ridges for straining the food, and has power-
ful circular muscles to squeeze the food back into the stomach, as well as
longitudinal m.uscles for relaxing, or opening, the gizzard. The pro-
ventriculus not only serves as a strainer, but also helps to comminute
the food, like the gizzard of a bird.
I04
ENTOMOLOGY
In most insects a cardiac valve guajrds the entrance to the stomach,
preventing the return of food to the gullet. This valve (Figs. 146, 151)
' cm
Fig. 150. — Alimentary tract of a moth. Sphinx, c, food reservoir; cl, colon; cm,
cascum; i, ileum; m, mid intestine; mt, Malpighian tubes; o, oesophagus; r, rectum; s, salivary
gland. — After Wagner.
is an intrusion of the stomodaeum into the mesenteron, forming a circu-
lar lip which permits food to pass backward, but closes upon pressure
from behind.
Mesenteron. — The ventriculus, otherwise known as the mid intestine,
or stomach, is usually a simple tube of large caliber,
as compared with the oesophagus or intestine, and into
the ventriculus may open glandular blind tubes, or
gastric ccBca (Figs. 147, 148) ; these, though numerous
in some insects, are commonly few in number and
restricted to the anterior region of the stomach. The
gastric caeca of Orthoptera secrete a weak acid which
emulsifies fats, or one which pa,sses forward into the
crop, there to act upon albuminoid substances. In
the stomach the food may be acted upon by a fluid
secreted by specialized cells of the epithehal wall.
In various insects, certain cells project periodically
into the lumen of the stomach as papillae, which by a
_ process of constriction become separated from the
valve of young muscid parent cells and mix bodily with the food. Thisphe-
/.^^provekScJiu^s^^^i nomenon takes place in the larva oiPtychoptera (van
valve. In an older Gchuchten), also in nymphs of Odonata (Necdham),
larva the valve pro- i i i r • i i
jects into the mid in- and IS probably of widespread occurrence among m-
I.evsky7'^^'''^°'^^" sects- The chief function of the stomach is absorp-
tion, which is effected by the general epithelium.
Physiologically, the so-called stomach of an insect is quite unlike the
stomach of a vertebrate, being more like an intestine.
Proctodaeum. — At the anterior end of the hind intestine there is
usually a pyloric valve, which prevents the contents of the intestine
ANATOMY AND PHYSIOLOGY
f05
from returning into the stomach. This valve may operate by means of
a sphincter, or constricting, muscle, or may, as in Collembola (Fig. 146),
consist of a backward-projecting circular ridge, or lip, which closes
upon pressure from behind.
In its primitive condition the hind intestine is a simple tube (Fig.
146). Usually, however, it presents two or even three specialized
regions, namely and in order, ileum, colon and rectum (Fig. 147). The
hind intestine varies greatly in length and is frequently so long as to be
thrown into convolutions (Fig. 152). The ileum is short and stout in
grasshoppers (Fig. 147); long, slender and convoluted in many carniv-
/'r^^
Pig. 152. — Digestive system of Belos-
toma. c, caecum; I, ileum; w, mid intestine;
mt, Malpighian tubes; r, salivary reservoir;
5, salivary gland. — After LocY, from the
American Naturalist.
Fig. 153. — Wall of mid intestine of silk-
worm, transverse section, b, basement mem-
brane; c, circular muscle; /, intima; I, longi-
tudinal muscle; n, n, nuclei of epithelial
cells; 5, secretory cell.
orous beetles; and quite short in caterpillars and most other larvae; its
function is absorption. The colon, often absent, is evident in Orthop-
tera and Lepidoptera and may bear {Benacus, Dytiscus, Silphidse,
Lepidoptera) a conspicuous caecal appendage (Figs. 150, 152) of doubt-
ful function, though possibly a reservoir for excretions. The colon
contains indigestible matter and the waste products of digestion, includ-
ing the excretions of the Malpighian tubes. The rectum (Fig. 147) is
thick-walled, strongly muscular and often folded internally. Its
office is to expel excrementitious matter, consisting largely of the indi-
gestible substances chitin, cellulose and chlorophyll. The rectum
terminates in the anus, which opens through the last segment of the
abdomen, always above the genital aperture.
io6
ENTOMOLOGY
g
Histology. — The epithelial wall of the alimentary tract is a single
layer of cells (Fig. 153), which secretes the intima, or lining layer, and
the basement membrane — a delicate, structureless enveloping layer.
The intima, which is continuous with the external cuticula, is chitinous
in the fore and hind gut (which are ectodermal in origin) , but not in the
mid gut (entodermal) , and usually exhibits extremely fine transverse
striae, which are due probably to minute pore canals. Surrounding
the basement membrane is a series of circular muscles and outside these
is a layer of longitudinal muscles in the mid gut. In
the fore gut the longitudinal muscles are frequently
under the circular muscles; and in the hind gut there
may be two layers of circular muscles with longitudinal
muscles running between them; but there are many
variations in the relative positions of the two kinds of
muscles in different kinds of insects. The circular
muscles serve to constrict the pharynx in sucking insects
and, in general, to squeeze backward the contents of the
alimentary canal by successively reducing its caliber.
The longitudinal muscles, restricted almost entirely to
the mid intestine, act in opposition to the constricting
muscles to enlarge the lumen of the food canal and in
addition to effect peristaltic movements of the stomach.
The intima of the crop is sometimes shaped into
teeth, and that of the proventricvilus is heavily chitin-
ized and variously modified to form spines, teeth or
ridges,
Peritrophic Membrane. — This membrane forms
an elastic tube inside the mid intestine and hind in-
testine; is derived usually from the epithelial cells
of the mesenteron; and is, in some instances at least,
renewed periodically. The peritrophic membrane,
found in ants, wasps, caterpillars, and larvae and adults
of many beetles, etc., is characteristic of insects that consume solid food
containing much hard, indigestible matter, and doubtless serves to pro-
tect the epithelium of the mid intestine from mechanical injury.
Salivary Glands. — In their simplest condition, the salivary glands
are a pair of blind tubes (Fig. 154), one on each side of the oesophagus
and opening separately at the base of the hypopharynx. Commonly,
however, the glands open through two salivary ducts into a common,
or evacuating, duct; a pair of salivary reservoirs (Fig. 155) may be
Fig. 154. — A sim-
ple salivary gland of
CcBcilius. c, canal; d,
duct; g, g, glandular
cells. — After Kolbe.
ANATOMY AND PHYSIOLOGY
107
present and the glands are frequently branched or lobed, and though
usually confined to the head, may extend into the thorax or even into
the abdomen. •
Many insects have more than one pair of glands opening into the
pharynx or oesophagus ; thus the honey bee has six pairs and Hymenop-
., b
- B.
Fig. 155. — Right salivary gland of cockroach, ventral
aspect, c, common duct; g, gland; h, hypopharynx; r,
-After MiALL and Denny.
reservoir.-
FiG. 156. — Histology of
salivary gland of Ccecilius,
radial section, b, basement
membrane; c, canal; g, g,
glandular cell; i, intima; n,
nucleus. — After Kolbe.
tera as a whole have as many as ten different pairs. Though all these
are loosely spoken of as salivary glands, it is better to restrict that
term to the pair of glands that open at the hypopharynx.
All these cephalic glands are evaginations of the stomodaeum (ecto-
dermal in origin) and consist of an epithelial layer with the customary
intima and basement membrane (Fig. 156). The nuclei are large, as is
usually the case in glandular cells, and
the cytoplasm consists of a dense
framework (appearing in sections as a
network) enclosing vacuoles of a clear
substanc^the secretion; the chitinous ,P'^- ^s 7. -One of the three-iobed
' salivary glands of a mosquito. The
intima is penetrated by fine pore canals middle lobe secretes the poison.— After
,1 1 1 • 1 ,1 .• Macloskie, from the American Nat-
through which the secretion passes, uraiist.
In many insects, notably the cockroach,
the common duct is held distended by spiral threads which give the duct
much the appearance of a trachea.
In herbivorous insects the saliva changes starch into glucose, as in
vertebrates; in carnivorous forms it acts on proteids and is often used
to poison the prey, as in the larva of Dytiscus. In the mosquito each
gland is three-lobed (Fig. 157) ; the middle lobe is different in appearance
from the two others and secretes a poisonous fluid which is carried out
io8
ENTOMOLOGY
along the hypopharynx. Though this poison is said to faciHtate the
process of blood-sucking by preventing the coagulation of the blood, its
primary use was perhaps to pre\»ent the coagulation of proteids in the
juices of plants.
Malpighian Tubes. — The kidney, or Malpighian, tubes, present in
nearly all insects, are long, slender, blind tubes opening into the intestine
immediately behind the stomach as a rule (Figs
147, 148) , but always into the intestine. The num-
ber of kidney tubes is very different in different in-
sects; Collembola have none, while Odonata have
fifty or more and Locustidae as many as one hun-
dred and fifty; commonly, however, there are four
or six, in Coleoptera, Lepidoptera and many other
Fig. 158. — Portion Pig. 159. — Cross-section of Malpighian tube of silkworm
of Malpighian tube of Bombyx tnori. b, basement membrane; c, crystals; 1, intima
caterpillar, Samia ce- I, lumen; n, nucleus; p, peritoneal layer. Greatly magnified.
cropia, surface view.
orders. Not more than six and frequently only four occur in the
embryo (Wheeler), though these few embryonic tubes may subsequently
branch into many.
The Malpighian tubes (Fig. 158) are evaginations of the proctodaeum
and are consequently ectodermal. A cross-section of a tube shows a
ring of from one to six or more large polygonal cells (Fig. 159), which
often project into the lumen of the tube; the nuclei are usually large and
may be branched, as in Lepidoptera. A chitinous intima, traversed by
pore canals, lines the tube, and a delicate basement membrane is present,
surrounded by a peritoneal layer of connective tissue. Furthermore,
the urinary tubes are richly supplied with tracheae. In function, the
Malpighian tubes are analogous to the vertebrate kidneys and con-
tain a great variety of substances, chief among which are uric acid and its
derivatives (such as urate of sodium and of ammonium), calcium oxalate
and calcium carbonate.
ANATOMY AND PHYSIOLOGY
109
Parts of the fat-body may also be concerned in excretion; thus the
fat-body in CoUembola and Orthoptera serves for the permanent storage
of urates.
7. Circulatory System
Insects, unlike vertebrates, have no system of closed blood-vessels,
but the blood wanders freely through the body
cavity to enter eventually the dorsal vessel, which
resembles a heart merely in being a propulsatory
organ.
Dorsal Vessel. — The dorsal vessel (Figs. 160,
164) is a delicate tube extending along the median
dorsal line immediately under the integument.
A simple tube in some larvae, it consists in most
adults chiefly of a series of chambers, each of- which
has on each side a valvular opening, or ostium
(Fig. 161), which permits the ingress of blood but
opposes its egress; within the chambers occur
other valvular folds that allow the blood to move
forward only. With few exceptions (Ephemeridae)
the dorsal vessel is blind behind and the blood can
enter it only through the lateral ostia.
Aorta. — The posterior, or pulsating portion
{heart) of the dorsal vessel is confined for the most
part to the abdomen; the anterior portion, or aorta,
extends as a simple attenuated tube through the
thorax and into the head, where it passes under
the brain and usually divides into two branches gel of beetk.^LMcanws.^^^
(Fig. 164), each of which may again branch. In ^o"^*^: «^' ^^^^y muscle; o.
\ , 7 , , 1 1 1 1 1 1 ostium.— After Straus-
the head the blood leaves the aorta abruptly and Durckheim.
enters the general body cavity;
Alary Muscles. — Extending outward from the "heart," or pro-
pulsatory portion, and making with the dorsal wall of the body a pericar-
dial chamber, is a loose diaphragm, formed largely by paired fan-like
muscles — the alary muscles (Figs. 160, 162). These are thought to assist
the heart in its propulsatory action.
Structure of the Heart.— The wall of the heart is remarkably thin,
and consists essentially of a muscular layer containing closely-set circular
or spiral fibers and separated longitudinal fibers, with scattered nucle-
ated cells among the fibers. This muscular tube is between two layers:
aio
ENTOMOLOGY
ail inner membrane, or sarcolemma, and an outer layer of elastic con-
nective tissue, the adventitia.
Pericardial Cells. Nephrocytes. — The pericardial cells occur gener-
ally in larvae and imagines in the vicinity of the heart, usually on each
side of the heart, and arranged frequently in longitudinal "garland-like"
Fig. i6i. — Diagram of a portion of the
heart of a dragon fly nymph, Epilheca.
o, ostium; v, valve; the arrows indicate
the course of the blood. — After Kolbe.
Fig. 162. — Diagrammatic cross-section of
pericardial region of a grasshopper, CEdipoda.
a, alary muscle; d, dorsal vessel; s, suspensory
muscles; sp, septum. — After Graber.
series. They vary greatly in position, number, form, size and contents,
and evidently bear some relation to the circulatory system; though
many functions have been assigned to them. In allusion to their
supposed excretory function, these cells have been named nephrocytes,
the term applying particularly to such cells as select and absorb acid
ammonia carmine, when that stain is injected into the living insect.
Ventral Sinus.— In many if not most insects a pulsatory septum
(Fig. 180, v) extends across the floor of the body cavity to form a sinus,
Fig. 163. — Blood corpuscles of a grasshopper, Slenobothrus. a-f, corpuscles covered
with fat-globules; g, corpuscle after treatment with glycerine, showing nucleus. — After
Graber.
in which the blood flows backward, bathing the ventral nerve cord as it
goes. This ventral sinus supplements the heart in a minor way, as do
also the local pulsatory sacs which have been discovered in the legs
of aquatic Hemiptera and the head of Orthoptera.
Blood. — The blood, or hcemolymph, of an insect consists chiefly of a
watery fluid, or plasma, which contains corpuscles or leucocytes. Though
ANATOMY AND PHYSIOLOGY
usually colorless, the plasma is sometimes yellow (Coccinellidae,
Meloidae), often greenish in herbivorous insects from the presence of
chlorophyll, and sometimes of other colors; often the blood owes its
hue to yellow or red drops of fat on the surface of the blood corpuscles
Fig. 163).
Haemocytes. — The corpuscles or hcBmocytes {leucocytes) are minute
nucleated cells, 6 to 30 /x in diameter, variable in form even in the same
species, but commonly (Fig. 163) round, oval or ovate in outline,
though often disk-shaped, elongate or amoeboid in form.
Function of the Blood. — The blood
of insects contains many substances,
including egg albumin, globulin, fibrin,
iron, potassium and sodium (Mayer),
and especially such a large amount of
fatty material that its principal function
is probably one of nutrition; the blood
of an insect contains no red corpuscles
and has little or nothing to do with the
aeration of tissues, that function being
relegated to the tracheal system.
Circulation.— The course of the cir-
culation is evident in transparent aquatic
nymphs or larvae. In odonate or ephe-
merid nymphs, currents of blood may be
seen (Fig. 164) flowing through the spaces
between muscles, tracheae, nerves, etc.,
and bathing all the tissues; separate Fig- 164.— Diagram to indicate the
. course of the blood in the nymph of a
outgomg and mcommg streams may be dragon fly, Epitheca. a, aorta; h.
distinguished in the antenna and legs; heart; the arrows show directions taken
° ° ' by currents of blood. — After Kolbe.
the returning blood flows along the sides
of the body and through the ventral sinus and the pericardial chamber,
eventually to enter the lateral ostia of the dorsal vessel. A circulation
of blood occurs in the wings of freshly emerged Odonata, Ephemerida,
Coleoptera, Lepidoptera, etc., the currents trending along the tracheae;
this circulation ceases, however, with the drying of the wings.
The chambers of the dorsal vessel expand and contract successively
from behind forward. At the expansion (diastole) of a chamber its ostia
open and admit blood; at contraction (systole) the ostia close, as well as
the valve of the chamber next behind, while the chamber next in front
expands, affording the only exit for the blood. The valves close partly
through blood-pressure and partly by muscular action.
112 ENTOMOLOGY
The rate of pulsation depends to a great extent upon the activity of
the insect and upon the temperature and the amount of oxygen or car-
bonic acid gas in the surrounding atmosphere. Oxygen accelerates the
action of the heart and carbonic acid gas retards it. A decrease of 8° or
io° C. in the case of the silkworm lowers the number of beats from 30 or
40 to 6 or 8 per minute. The more active an insect, the faster its heart
beats.
The rate of pulsation is very different in the different stages of the
same insect. Thus in Sphinx ligustri, according to Newport, the mean
number of pulsations in a moderately active larva before the first molt
is about 82 or 83 per minute; before the second molt, 89, sinking to 63
before the third molt, to 45 before the fourth, and to 39 in the final
larval stage; but the force of the circulation increases as the pulsations
decrease in number. During the quiescent period immediately preced-
ing each molt, the number of beats is about 30. In the pupal stage
the number sinks to 22, and then lowers until, during winter, the pulsa-
tions almost cease. The moth in repose shows 41 to 50 per minute, and
after flight as many as 139.
8. Fat-Body
The fat-body appears (Fig. 165) as many-lobed masses of tissue filling
in spaces between other organs and occupying a large part of the body
cavity. The distribution of the fat-body is to a certain extent definite,
however, for the fat-tissue conforms to the general segmentation and is
arranged in each segment with an approach to symmetry. Much of
this tissue forms a distinct peripheral layer in each segment, and masses
of fat-body occur constantly on each side of the alimentary tract and
also at the sides of the dorsal vessel, in the latter case forming the
pericardial fat-body.
Fat-Cells. — The fat-cells (Fig. 166) are large and at first more or
less spherical, with a single nucleus (though there are said to be two in
Apis and several in Musca), but the cellular structure of the fat- tissue is
often difficult to make out because the cells are usually filled with glob-
ules of fat (Fig. 167), while old cells break down, leaving only a disorderly
network. The fat-cells sometimes contain an albuminoid substance, and
usually the fat-body includes considerable quantities of uric acid or its
derivatives, frequently in the form of conspicuous concretions.
Functions. — The physiology of the fat-system is still obscure.
Probably the fat-body combines several functions. In caterpillars and
other larvae it furnishes a reserve supply of nutriment, at the expense of
ANATOMY AND PHYSIOLOGY
113
Fig. 165. — Transverse section of the abdomen of a caterpillar, Pieris rapm. b, blood cor-
puscles; c, cuticula; d, dorsal vessel; /, fat-body; g. ganglion; h, hypodermis; I. leg;w,
muscle; mi, mid intestine, containing fragments of cabbage leaves; mt, Malpighian tube; s,
silk gland; sp, spiracle; tr, trachea.
which the metamorphosis takes place; the amount of fat increases as
the larva grows, and diminishes in the pupal stage, though some of it
lasts over to furnish nourishment for the
imago and its germ cells. The gradual
accumulation of uric acid and urates in
the fat-body indicates an excretory func-
tion, particularly in Collembola, which
have no Malpighian tubes. The intimate ^^^ i66.-Fat-ceiis of a eater-
association between the ultimate tracheal pillar, Pieris. a, cells filled with
, , r . ^ 11 1 J drops of fat; 5, cell freed of fat-drops,
branches and the fat-body has led some showing nucleus.— After Kolbe.
authorities to ascribe a respiratory func-
tion to the latter. A close relation of some sort exists also be-
tween the fat-system and the blood-system; fat-cells are found free
in the blood, and the blood corpuscles originate in the thorax and
114
ENTOMOLOGY
abdomen from tissues that can scarcely be distinguished from fat-
tissues. The corpuscles {leucocytes, or phagocytes) which in some insects
absorb effete larval tissues during metamorphosis have been by some
authors regarded as wandering fat-cells. Cells constituting the peri-
cardial fat-body are attached to the
lateral muscles {alary muscles) of the
dorsal vessel, but almost nothing is
definitely known as to their function.
CEnocytes. — Associated with the
fat-body proper and with tracheae as
well are the peculiar yellow cells known
as cenocytes (Fig. i68), that occur in
abdominal segments of larvae. These
cells are enormous in size as compared
with all other insect-cellsexceptingova,
and are essentially isolated from one
Fig. 167.— Section through fat-body of a another, though grouped among tra-
siikworm. showing nucleated cells, loaded cheal branches into loosc clusters, One on
with drops of fat.
each side of a spiracle-bearing segment.
After arising from the primitive ectoderm the cenocytes never divide,
but gradually increase in size (Wheeler), and their size is in a general way
proportional to that of the fat-body.
Their function has been problematical until recently. Many ob-
servers have regarded them as ductless glands, having seen "microscop-
ical exudations around the periphery of the cytoplasm,
especially at times when the nucleus is greatly rami-
fied, and therefore manifesting its great activity"
(Glaser).
R. W. Glaser has thrown light upon the nature of
the oenocytic fluid. By using three-year-old caterpillars
of the leopard moth, Zeuzera pyrina, which have a
great amount of fatty tissue and correspondingly large
cenocytes, he was able to extract enough of the fluid
for chemical experiments. He found by carefully con- ^^^- 168.— CEno-
-^ -^ cytes and accom-
ducted tests that the fluid had the power of oxidizing panying tracheae,
fats, by means of enzymes known as oxidases (though siik^o^.^"^^'^ °^ ^
no fat-splitting enzyme, or lipase, was present), and
concluded that the secretion of the cenocytes is used to oxidize the
reserve food stored up by the larva in the form of fat.
Photogeny. — This phenomenon appears sporadically and by various
means in protozoans, worms, insects, fishes and other animals. Lumi-
ANATOMY AND PHYSIOLOGY 115
nosity in insects, though sometimes merely an incidental and pathologi-
cal effect of bacteria, is usually produced by special organs in which
hght is generated, probably by the oxidation of a fatty substance.
There are not many luminous insects. Those best known are the
Mexican and West Indian beetles of the genus Pyrophorus (Elateridse) ,
in which the pronotum bears a pair of luminous spots, and the common
fireflies (Lampyrid^). In Lampyridae the light is emitted from the
ventral side of the posterior abdominal segments, and the structure of
the photogenic organ is essentially the same throughout the family.
In Photinus this organ (Fig. 169) consists of two layers; a ventral photo-
genic layer and a dorsal reflecting layer. The latter, white and opaque,
consists of polygonal cells containing large quantities of crystals of ur-
ates; the former layer is composed
of tracheal structures and inter-
vening parenchyma cells. The
tracheae branch profusely in the
photogenic layer, where the larger
air-tubes are each surrounded by
a more or less cylindrical mass of
cells; tracheal branches penetrate
between the cells of each cylinder,
at the edge of which they pass into
tracheoles which penetrate the ^
photogenic tissue and anastomose ^^^ ,69.-Transverse section of portion of
with those of adjacent cylinders; photogenic organ of a firefly, Photinus. c,
1 c A-\^ 4. „„V,^^lo,. cylinder;^, photogeniclayer;*-, reflecting layer;
in the meshes of the tracheolar ^/trachekf— After Townsend.
network is agranular substance of
fatty nature ("differentiated fat-body"), the oxidation of which is the
source of the luminosity, it is inferred. The photogenic tissues of
Photinus, after being dried and kept in sealed tubes, have retained their
photogenic power for more than eighteen months, glowing after this
interval upon the " application of water in the presence of air or oxygen "
(McDermott). Three factors are involved in the production of the
light: a substance to be oxidized, oxygen and water.
Professor W. E. Burge has found that the catalase content of a
luminous insect where oxidation is presumably more intense is greater
than that of a non-luminous insect where oxidation is less intense.
The rays emitted by the common fireflies are remarkable in being
almost entirely light rays. According to Young and Langley, the radia-
tions of an ordinary gas-flame contain less than three per cent, of visible
Il6 ENTOMOLOGY
rays, the remainder being heat or chemical rays, of no value for illumina-
ting purposes; while the light-giving efficiency of the electric arc is only
ten per cent, and that of sunhght only thirty-five per cent. The luminous
efficiency of the firefly is, however, not much under one hundred per
cent.; in Photuris pennsylvanica it is about ninety-two per cent., accord-
ing to Coblentz — an efficiency as yet unapproached by artificial means.
The actinic power of the light is so slight that it affects a photographic
plate only after a long exposure. . Coblentz, who has applied most
refined methods of measurement to the radiation of fireflies, found
that exposures of one to five hours were necessary with the spectro-
graph. He was unable to detect any infra-red radiation; the thermal
radiation, if present, being immeasurably small as yet. The intensity
of the glow averages 3'^o>ooo candle power in our common fireflies,
according to Coblentz.
This luminosity serves to bring the sexes together. "The male flies
over the tops of the grasses, weeds, etc., dropping down between them
and flashing; any females that come within the range of his flash, answer
by their slower flash; if the male sees this answering flash from one, he
approaches her, flashes again, to which she answers, and he then finally
locates her definitely by means of subsequent flashes," as McDermott
says. He found that he coifld get responses from the females by imi-
tating the flash of the male with a small electric bulb or even with a com-
mon safety match, and that he could deceive the males also by flashing
the tiny electric fight after the manner of the female.
Synchronism. — Several observers in the PhiHppines and East
Indies have seen the phenomenon of thousands of fireflies flashing
exactly in unison; all the fireflies in the same tree, for example, flashing
simultaneously (105-109 flashes per minute, in one instance), with regular
intervals of darkness. This rare phenomenon, to which Professor E. S.
Morse called attention, has attracted considerable interest in the
columns of Science. There seems to be no doubt as to the accuracy of
the observations, but an explanation as to how the synchronism is
effected and regulated is still lacking. The phenomenon can hardly be
due to chance when thousands of individuals are involved. The
fireflies referred to, in Siam and the Philippines, belong to the genus
Calaphotia (0. A. Reinking).
9. Respiratory System
In insects, as contrasted with vertebrates, the air itself is conveyed to
the remotest tissues by means of an elaborate system of branching air-
ANATOMY AND PHYSIOLOGY
117
tubes, or trachece, which receive air through paired segmentally-arranged
spiracles. Each spiracle is commonly the mouth of a short tube which
opens into a main tracheal trunk (Fig. 170) extending along the side of
the body. From the two main trunks branches are sent which divide
and subdivide and terminate in extremely dehcate tubes, which pene-
trate even between muscle fibers; between the ommatidia of the com-
pound eyes and possibly enter cells. In
most cases each main longitudinal trunk
gives off in each segment (Fig. 171) three
large branches: (i) an upper, or dorsal,
branch which goes to the dorsal muscles;
(2) a middle, or visceral, branch, which
supplies the alimentary tract and the
reproductive organs; (3) a lower, or
ventral, branch, which pertains to the
ventral ganglia and muscles.
In many swiftly flying insects (dragon
flies, beetles, moths, flies and bees) there
occur tracheal pockets, or air-sacs, which
were formerly and erroneously supposed
to diminish the weight of the insect, but
are now regarded as simply air-reser-
voirs. Sacs filled with air lessen the
specific gravity of an insect in a fluid
medium; but do not increase the buoy-
ancy of an insect in the air, unless the
contained air is warmer than the sur-
rounding air; and in the case of birds,
it has been found that the air contained
in the bones, though warmer than the
„ ,. , ... Fig. 170. — Tracheal system of an
SUrrOUndmg medmm, has no appreciable insect, a, antenna; b, brain; I, leg;
effect on flight. "• ^^^^^ ^°'"^; ^' palpus; s, spiracle;
^ ' ^ St, spiracular, or stigmatal, branch; t,
T3rpeS of Tracheation. Two types main tracheal trunk; ?;, ventral branch;
r , 1 , , T .• • 1 1 J- i>s, visceral branch. — After Kolbe.
of tracheal system are distmguished tor
convenience: (i) the primary, open, or holopneustic type described above,
in which the spiracles are functional; (2) the secondary, closed, or apneus-
tic type, in which the spiracles are either functionless or absent. This
type is illustrated in Collembola and such aquatic nymphs and larvae as
breathe either directly through the skin or else by means of gills. The
two types are connected by all sorts of intermediate stages.
Il8 ENTOMOLOGY
Tracheal Gills. — In many aquatic nymphs and larvae the spiracles
are suppressed (though they become functional in the imago) and res-
FiG. 171. — Diagrammatic cross-section of the thorax of an insect, a, alimentary canal;
d, dorsal vessel; g, ganglion; s, spiracle; w, wing; i, dorsal tracheal branch; 2, visceral
branch; 3, ventral branch.
piration is effected by means of gills; these are cuticular outgrowths
which contain tracheas and tracheoles and are commonly lateral or
caudal in position. Lateral tracheal gills
are highly developed in ephemerid
nymphs (Fig. 172), in which a pair occurs
on some or all of the first seven segments
of the abdomen; a few genera have
cephalic or thoracic gills. Larvae of Tri-
choptera have paired abdominal gills
varying greatly in form and position,
and Perlidae often have paired thoracic
gills. Caudal tracheal gills are conspicu-
ous in nymphs of damsel flies (Fig. 173)
as three foliaceous appendages. A few
coleopterous larvae of aquatic habit, as
Gyrinus and Cnemidotus, possess tracheal
Jnof a'M^ %Ty„S, 'Xi-S g"'^- ^ ^o also caterpillars of the genus
variabilis. Enlarged. Pam/>owya; (Fig. 1 74) , which f eed on the
leaves of several kinds of water plants.
Though manifold in form, tracheal gills are usually more or less
foliaceous or filamentous, presenting always an extensive respiratory
surface; their integument is thin and the tracheae spread closely beneath
ANATOMY AND PHYSIOLOGY
119
Fig. 173. — Caudal
gills of a damsel fly
nymph, enlarged.
it. These adaptations are often supplemented by waving movements of
the gills, as in May fly nymphs, and by frequent movements of the
insect from one place to another.
Especially noteworthy are the rectal tracheal gills of odonate nymphs.
In these insects the lining of the rectum forms numerous papilla) or
lamellae, which contain a profusion of delicate tra-
cheal branches; these are bathed by water drawn
into the rectum and then expelled, at rather irregu-
lar intervals. A similar rectal respiration occurs
also in ephemerid nymphs and mosquito larvae.
A few forms, chiefly Perlidae, are exceptional in
retaining tracheal gills in the adult stage; in some
imagines they are merely vestiges of the nymphal gills, but in others,
such SiS Pteronarcys (Fig. 19), which habitually dips into the water
and rests in moist situations, the gills probably supplement the spiracles.
Further details on the respiration of aquatic insects
are given in Chapter IV.
Blood-gills. — In a few aquatic larvae, Simulium
and Chironomus for example, there are thin tubular
evaginations of the integument known as blood-gills,
into which the blood flows. In trichopterous larvae
(caddis-worms) the blood-gills are eversible. Some
authors regard the ventral eversible sacs of Scolo-
pendrella and Thysanura, as well as the vesicles of
the ventral tube of Collembola, as blood-gills.
Spiracles. — The paired external openings of the
tracheae, termed spiracles or stigmata, occur on the
sides of the thorax and abdomen; there being not
more than one pair to a segment, though not all
segments bear them. As a rule, there are two tho-
racic and eight abdominal pairs; these belonging to
Fig. 174. — Cater- the mesothorax, metathorax, and first eight abdom-
£l.a/?. JZTIZ inal segments, respectively. Adult insects do not
cheai gills. Length, 15 have morc than ten pairs, with the exception of
mm. — After Hart. . ^ e \
Japyx (see page 60, footnote).
The spiracles, variable in position, are situated usually between two
segments of the body; but often at the anterior borders of the seg-
ments to which they belong; though they may occur farther back on
the segments.
In most embryo insects there are eleven pairs of spiracles — three
I20 ENTOMOLOGY
thoracic and eight abdominal; but in adults the prothoracic pair is
almost always suppressed. (See page 60.)
Though tracheae are absent in most Collembola, Sminthurides
aquaticus has tracheae in the head, which open through
a pair of spiracles on the posterior part of the head,
there being a spiracle on each side of the neck. Two
other species of Collembola, Sminthurus fuscus and
Actaletes neptuni, are likewise known to have such a
tracheal system, limited to the head.
The spiracles are usually provided with bristles,
hairs or other processes to exclude dust; or the hairs
of the body may serve the same purpose, as in Lepidop-
tera and Diptera; in many beetles the spiracles are pro-
tected by the elytra; but in other beetles and in many
Hemiptera and Diptera the spiracles are unprotected
externally. Larvae that live in water or mud may have
Fig. 175.— Larva spiracles at the end of a long tube, which can be
^ciavipes! ^sh^winl. thrust up into the pure air; this is true of the dipter-
respiratory tube.— Q^g larvag of Eustalis, BUtacomorpha (Fig. 175) and
Natural size. — After i \ o i ^/
Hart. CuUx (Fig. 232).
Closure of Spiracles. — As a rule, a spiracle is opened
and closed periodically by means of a valve, operated by a special occ/w^or
muscle. In dipterous larvae the closure is effected by the contraction of
Fig. 176. — Apparatus for closing the spiracular trachea in a beetle, Lucanus. A,
trachea opened; B, closed; b, bow; bd, band; c, external cuticula; I, lever; m, muscle; s,
spiracle; t, trachea. — After Judeich and Nitsche.
a circular muscle, but Coleoptera and Lepidoptera, among other insects,
have a somewhat complex apparatus for closing the trachea immediately
behind the spiracle. Thus, in the stag-beetle, a crescentic bow (Fig.
176, b) extends half around the trachea, and the rest of the circumfer-
ence is spanned by a lever (I) and a band {bd) ; these three chitinous parts.
ANATOMY AND PHYSIOLOGY
articulated together, form a ring around the trachea. Furthermore, a
muscle (m) connects the lever and the band. As the muscle shortens,
the lever turning upon the end of the band as a fulcrum, pulls the bow
Fig. 177. — Structure of a
trachea, h, tracheal hypo-
dermis; i, intima; I taenidium.
Fig. 178. — Tracheolar end-network from silk gland
of Porthelria dispar. p, peritracheal membrane; t,
tracheal capillary. — After Wistinghausen.
toward the lever and band until the enclosed trachea is pinched together.
When the muscle relaxes, the trachea opens by its own elasticity.
Structure of Tracheae. — The tracheae originate in the embryo as
simple in-pocketings of the outer germ layer, or ectoderm, and from
Pig. 179. — Transverse sections of abdominal segments to illustrate respiratory move-
ments. A, cockroach (Blalta); B, bee (Bombus); s, sternum; t, tergum. The dotted lines
indicate positions of terga and sterna after expiration; the continuous lines, after inspira-
tion.— After Plateau.
these the countless tracheal branches are derived by the same process of
invagination. The lining membrane of a trachea is, then, continuous
with the external cuticula, and the cellular wall of a trachea is continu-
ous with the rest of the hypodermis. This wall consists of a layer of
polygonal cells (Fig, 177) fitting closely together as a pavement epithe-
lium. The chitinous lining, or intima, is thickened at regular intervals
to form thread-like ridges, which course around the inner circumference
122 ENTOMOLOGY
in essentially a spiral manner, though the continuity of the so-called
spiral thread is frequently interrupted. These elastic threads, or
tcBuidia, serve to keep the trachea open without affecting its flexibility.
On the outer surface of the epithelium is a thin structureless basement
membrane.
Tracheoles. — The ultimate divisions of the air-tubes (Fig. 178) are
extremely delicate tubes, or tracheoles, which rarely end bhndly, but
anastomose with one another, forming a capillary network of confluent
tubes, measuring less than o.ooi mm. in diameter, and filled, not with
air, but with a fluid. Respiration takes place doubtless by means of
the tracheoles rather than the trachese.
In a caterpillar, these capillary tubes spread out over the surface of
the cells of the silk-glands, according to Wistinghausen; and penetrate
into the gland-cells themselves, according to Holmgren; other authors
differ also as to the relation of the ultimate branches of the air-tubes to
the cells which they serve.
The tracheoles consist of (i) a well developed peritracheal membrane,
which spreads out web-like between the bases of the tubes; and (2) a
chitinous intima without taenidia; the tracheoles being connected with
the tracheae proper by means of (3) transition cells.
Unlike tracheae, the tracheolar tubes do not arise directly by in-
vagination, but develop each within a single cell of the epithelium of
a trachea.
Respiration. — The external signs of respiration are the regular open-
ing and closing movements of some of the spiracles and the rhythmic
contraction and expansion of the abdomen. During contraction, the
dorsal and ventral walls approach each other (Fig. 179) and during
expansion they separate. The tergum moves more than the sternum
in Coleoptera and Heteroptera, and vice versa in Locustidae, Odonata,
Diptera and aculeate Hymenoptera. The width of the abdomen usu-
ally'changes but little during respiration, for the tergal and sternal
movements are taken up by the pleural membranes which, as in the
grasshopper, infold at contraction and straighten out at expansion.
Other respiratory movements occur, but they are of minor importance.
The rate of respiration increases or diminishes with the activity of
the insect and with temperature and other conditions. In six specimens of
Melanoplus diferentialis, held between the fingers, the thoracic spiracles
opened and closed respectively 34, 43, 45, 54, 60 and 61 times per
minute. Four individuals of M . femur -rubrum under the same circum-
stances gave 70, 78, 90 and 92.
ANATOMY AND PHYSIOLOGY
23
,'k
At expansion inspiration takes place, and at contraction expiration
occurs. In the grasshopper, the thoracic spiracles open almost simul-
taneously with the expansion of the abdomen. Contraction is effected
by special vertical expiratory muscles (Fig. 180), but expansion is due
to the elasticity of the abdominal wall, as a rule; this is the reverse of
what occurs in mammals, where expiration is passive and inspiration
active. Inspiratory muscles are
found, however, in Locustidae, Tri-
choptera and Hymenoptera.
Though the respiratory move-
Hients of an insect may be studied
with a hand-lens, a more precise
method is that of Plateau — the chief
authority on insect physiology — who
made use of the stereopticon to pro-
ject an enlarged profile of the insect
upon a screen, on which could be
marked the different contours of the
abdomen at its phases of inspiration
and expiration.
The way in which the air reaches fig. i 80.— Diagrammatic cross-section
the finest tracheal branches is not of abdomen of a grasshopper, rroz-idacn^.
a, dorsal septum, or diaphragm; e*, expira-
Clearly ascertained, but it is thought tory muscle; /, fat-body; g, gangHon; K
.•i-.-r j-ii-T- 4-u u heart; in, inspiratory muscle; v, ventral
that air is forced into these tubes by ^.p^^^, ^eiow which is the ventral sinus.
pressure from the abdominal muscles, The dorsal and ventral septa rise and fall
. . periodically. — After Graber.
while its escape through the spiracles
is being prevented by the compression of the stigmatal tracheae.
The respiratory movements are entirely reflex and are independent
of the brain or suboesophageal ganglion, for they continue after decapi-
tation and even in the detached abdomen of a grasshopper or dragon
fly. Each ventral ganglion of the body is an independent respiratory
center for its particular segment.
10. Reproductive System
The sexes are always separate in insects, hermaphroditism occurring
only as an abnormal condition. The sexual organs, situated in the ab-
domen, consist essentially of a pair of ovaries or testes and a pair of ducts
(oviducts or seminal ducts, respectively). Primitively, the ducts open
separately, as they still do in Ephemeridae, but in almost all other insects
124
ENTOMOLOGY
the two ducts enter a common evacuating duct {vagina or ejaculatory
duct). The vagina commonly opens just behind the eighth abdominal
sternite, and the ejaculatory duct behind the ninth.
Fig. i8i. — Reproductive system of male
beetle, Melolontha. a, accessory gland; c, copu-
latory organ; d, ejaculatory duct; s, seminal
vesicle; t, testis; 2/,vas deferens. — After Kolbe,
Fig. 182. — Reproductive system of
male Lepidoptera. a, accessory gland;
d, ejaculatory duct; /, united testes; v,
vas deferens. — After Kolbe.
Homologies. — As in other animals, the reproductive organs are
homologous in the two sexes. Thus:
Male
Female
Testes = Ovaries
Seminal ducts = Oviducts
Ejaculatory duct = Vagina
Seminal vesicle = Seminal receptacle
Accessory glands = Accessory glands
Penis and accessories = Ovipositor
Male Organs.- — Each testis, though sometimes a single blind tube, is
usually a group of tubes or sacs (Fig. 181), testicular follicles , which open
into a seminal duct (vas deferens) . In most Lepidoptera the testes are
secondarily united into a single mass (Fig. 182) as also in Locustidae.
The two seminal ducts enter the common ejaculatory duct, which termi-
nates in the intromittent organ, or penis. Often each vas deferens is
dilated near its mouth into a seminal vesicle, or reservoir; or there may be
only a single seminal vesicle, arising from the common duct. One or
more pairs of glands opening into the vasa deferentia or the ductus
ejaculatorius secrete a fluid which mixes with the spermatozoa and
oftentimes unites them into packets, known as spermatophores.
All these parts are subservient to the formation, preservation and
emission of the spermatozoa. These minute, thread-like bodies (Fig.
ANATOMY AND PHYSIOLOGY
183) arise in the testicular follicles from a germinal epithelium, and
consist, as in vertebrates, of a head, middle-piece and a vibratile tail —
without entering into the liner structure.
Female Organs. — Each ovai^y (Fig. 184) consists of one or more
tubes opening into an oviduct. The two oviducts enter a common duct,
the vagina, which opens to the exterior, often through an ovipositor.
Frequently the vagina is expanded as a pouch,
or bursa copulatrix, though in Lepidoptera
the bursa and the vagina are distinct from
each other and open separately (Fig. 185).
In most insects a dorsal evagination of the
vagina forms a seminal receptach, or sperma-
theca, from which spermatozoa emerge to
fertilize the eggs. The accessory glands,
either paired or single, provide a secretion for
attaching the eggs to foreign objects, cement-
ing the eggs together, forming an egg-capsule,
etc.
In each ovarian tube, or ovariole, are found
ova in successive stages of growth, the largest
and oldest ovum being nearest the oviduct.
In the primitive type of egg- tube, as in Thy-
sanura and Orthoptera (Fig. 186, A) every
chamber contains an ovum; in more special-
ized types, every other chamber contains a
nutritive cell instead of a germ cell, the nutri-
tive cells serving as food for the adjacent ova {B) ; or the nutritive cells,
instead of alternating with the ova, may be collected in a special
chamber, beyond the ovarian chambers (C). An egg-tube is usually
prolonged distally as a terminal filament or suspensor, the free end of
which is attached near the dorsal vessel.
Ovaries and testes arise from indifferent cell or primitive germ cells,
which are at first exactly alike in the two sexes. In the female, certain
of these cells form ova and others form a, follicle around each ovum (Fig.
187). In the male, the primary germ cells form cells termed spermato-
gonia; each of these forms a spermatocyte, and this gives rise to four
spermatozoa.
Hermaphroditism. — The phenomenon of hermaphroditism, defined
as "the union, real or apparent, of the two sexes in the same individual,"
occurs among insects only as an extremely rare abnormality (except in
Fig. 183. — Spermatozoa.
A, grasshopper; B, cockroach,
Blatla; C, beetle, Copris. — Af-
ter BiJTSCHLi and Ballowitz.
126
ENTOMOLOGY
Termitoxinia, mentioned beyond). Speyer estimated that in Lepidop-
tera only one individual in thirty thousand is hermaphroditic. Bertkau
(1889) Hsted 335 hermaphroditic arthropods, of which 8 were crusta-
ceans, 2 spiders, 2 Orthoptera, 8 Diptera, 9 Coleoptera, 51 Hymenoptera
and 255 Lepidoptera. The large proportion of Lepidoptera is due in
great measure to the fact that they are collected oftener thaa 'other
insects (excepting possibly Coleoptera) and that sexual dimorphism
Fig. 184. — Reproductive system of queen
honey bee. a, accessory sac of vagina; h,
bulb of stinging apparatus; c, colleterial, or
cement, gland; o, ovary; od, oviduct; p,
poison glands; pr, poison reservoir; r, recep-
taculum seminis; re, rectum; v, vagina. —
After Leuckart.
Fig. 185. — Reproductive system of
female Lepidoptera. b, bursa copulatrix; /,
terminal filament; g, cement glands; o, o,
ovaries; od, oviduct; r, receptaculum
seminis; v, vagina; vs, vestibule, or entrance
to bursa. — After Kolbe.
is so prevalent in the order that hermaphrodites are easily recognized.
The most common kind of hermaphroditism is that in which one
side is male and the other female, as in Fig. 188. Bertkau found this
right-and-left hermaphroditism in 153 individuals. In other instances
the antero-posterior kind may occur, as when the fore wings are of one
sex and the hind wings of the other; rarely, the characters of the two
sexes are intermingled.
Hermaphroditic insects are such rarities that very few of them have
been sacrificed to the dissecting needle in order to determine whether the
phenomenon involves the primary organs as well as the secondary
sexual characters. Where dissections have been made it has been
found usually that hermaphroditism does extend to the reproductive
ANATOMY AND PHYSIOLOGY
127
organs themselves. Thus a butterfly with male wings on the right side
and female wings on the left would have a testis on the right side of the
abdomen and an ovary on the left side.
True hermaphroditism, existing "only when the essential organs of
reproduction are united in one individual,"
and are functional, is said to occur nor-
mally in a peculiar wingless termitophilous
fly, Termitoxinia. Other instances of her-
maphroditism among insects are, strictly
Fig. 186. — Types of ovarian
tubes. A , without nutritive cells ;
B, with alternating nutritive and
egg-cells; C, with terminal nutri-
tive chamber, c, terminal chamber;
e, egg-cell; e/>, follicle epithelium;
/, terminal filament; s, strands
connecting ova with nutritive
chamber; y, yolk, or nutritive
cells. — Prom Lang's Lehrbuch.
Fig. 187. — Ovum of a butterfly, Vanessa, inits fol-
licle, e, follicle epithelium; g, germinal vesicle; n,
branching nucleus of nutritive cell; o, ovum. — After
WOODWORTH.
speaking, examples of gynandromorphism,
in which secondary sexual characters of
both sexes occur in the same individual.
A gynandromorph often has ovaries and
testes at the same time, but both are not
functional.
Parthenogenesis. — Reproduction without fertilization is a normal
phenomenon in not a few insects. This parthenogenesis may easily be
observed in plant lice. In these insects there are many successive
broods consisting of females only, which bring forth living young; at
definite intervals, however, and usually in autumn, males appear also,
and fertilized eggs are laid which last over winter. This cycKc reproduc-
tion, by the way, is known as heterogeny. Among Hymenoptera,
parthenogenesis is prevalent, usually alternating with sexual reproduc-
tion, as in many Cynipidae. In some Cynipidae, however, males are
128
ENTOMOLOGY
Pig. 1 88. — Gynandromorphic gipsy moth,
Porthelria dispar; right side, male; left, female.
Natural size. — After Taschenberg from Hert-
wig's Lehrbuch.
unknown; such is the case also in some Tenthredinidae. The statement
has long been made that the unfertihzed eggs of worker ants, bees and
wasps produce invariably males; it has been found, however, that
the parthenogenetic worker eggs of the ant Lasius niger may produce
normal workers (Reichenbach,
Mrs. A. B. Comstock).
In the honey bee, unfertil-
ized eggs produce always males;
and it is at present rather gen-
erally believed that drones are
not produced from fertilized
eggs.
Professor A. F. Shull deter-
mined experimentally that un-
fertilized eggs of the thysanop-
teran, Anthothrips verhasci pro-
duce only males; and concluded
also that fertilized eggs produce only females. Parthenogenesis has
been recorded as occurring also in a few moths, some Coccidae and
many Thysanoptera.
Paedogenesis. — In Miastor and a few other genera of Itonididae
young are produced by the larva. This extraordinary form of partheno-
genesis is termed pedogenesis, and is limited apparently to the family
Itonididae. The paedogenetic
larvae of Miastor (Fig. 189)
develop before the oviducts
have appeared and escape by
the rupture of the mother.
After several successive gener-
ations of this kind the result-
ing larvae pupate and form normal male and female flies .
An excellent account of Miastor has been given by Dr. Felt, who
has discovered this remarkable genus in New York State.
The pupa of a species of Chironomus occasionally deposits unfer-
tihzed eggs, which develop, however, in the same manner as the
fertilized eggs of the species.
Fig. 189. — Young paedogenetic larvae of Miastor
in the body of the mother larva. Greatly enlarged.
— After PagenstecheR.
CHAPTER III
DEVELOPMENT
I. Embryology
Ovum. — The ovum of an insect, as of any other animal, is a single
cell (Fig. 190), witha large nucleus (germinal vesicle), a \a,rge nucleolus,
nutritive matter, or yolk {deulo plasm) , contained in cytoplasm, and a
cell wall {vitelline membrane) secreted by the ovum.
The egg-shell, or chorion, is secreted around the
ovum by surrounding ovarian cells.
Maturation. — As a preparation for fertilization
the germinal vesicle divides twice, forming two
polar bodies, and as the first of these bodies may
itself divide, there result four cells; three of these,
however — the polar bodies — are minute and rudi-
mentary.
These phenomena of ovogenesis are paralleled
in the development of the spermatozoa, or sperma-
togenesis; for the primary spermatocyte gives rise
to two secondary spermatocytes, and these to four
spermatids, each of which forms a spermatozoon.
By means of this maturation process the number
of chromosomes in the egg-nucleus is reduced to
half the number normal for somatic cells (body
cells as distinguished from germ cells). A simi-
lar reduction occurs also during the develop-
ment of the spermatozoon, and when sperm-nucleus
and egg-nucleus unite, the resulting nucleus con-
tains the normal number of chromosomes. The
meaning of these reduction phenomena — highly
important from the standpoint of heredity — is a
much debated subject.
Fertilization. — As the eggs pass through the
vagina, they are capable of being fertihzed by
■ spermatozoa, previously stored in the seminal receptacle. Through
the micropyle of the chorion one or more spermatozoa enter and a
9 129
Pig. 190. — Sagittal
section of egg of fiy,
Musca, in process of fer-
tilization, c, chorion; d,
dorsal; m, micropyle,
with gelatinous exuda-
tion; p, male and female
pronuclei, before union;
pb, polar bodies; pr,
peripheral protoplasm;
V, ventral; vt, vitelline
membrane ; y, yolk. —
After H E N K I N G and
Blochmann.
I30
ENTOMOLOGY
Fig. 191. — Equatorial section of egg of a beetle,
Clytra Iceviuscida. b, blastoderm; 5, germ band;
y, yolk granule; yc, yolk cell.- — After Lecaillon.
sperm nucleus unites with the egg-nucleus to form what is known as
the segmentation nucleus. Through this union of nuclear substances
the qualities of the two parents are combined in the offspring.
Needless to say, the minute
details of the process of fertili-
zation are of the highest bio-
logical importance.
Blastoderm. — In an arthro-
pod ovum the yolk occupies a
central position {centrolecithal
type), being enclosed in a thin
layer of protoplasm. From the
segmentation nucleus just men-
tioned are derived many nuclei,
some of which migrate out-
ward with their attendant pro-
toplasm to form with the
original peripheral protoplasm
a continuous cellular layer, the
blastoderm (Fig. 191).
Germ Band.— The blastoderm, at first of uniform thickness, be-
comes thicker in one region, by cell multiplication, forming the germ
hand {primitive streak, etc.); this appears in surface view as an oval
or elongate area, denser than the remaining blastoderm, with which
it is, of course, continuous.
Gastmlation. — The germ band next infolds along the median line,
appearing in cross-
section as in Fig. 192 ;
the two lips of the
median groove dost to-
gether over the invagi-
nated portion and
form an outer layer, or
ectoderm (Fig. 193),
while the invagi-
nated portion spreads
out as an inner layer, which is destined to form two layers, known
respectively as entoderm and mesoderm. This formation of two primary
germ layers by invagination or otherwise is termed gastrulation; it is
an important stage in the development of all eggs, and among insects
several variations of the process occur.
Fig. 192. — Transverse section of germ band of Clytra at
gastrulation. g, germ band; «, inner layer. — After LecaillON.
DEVELOPMENT
131
Amnion and Serosa. — Meanwhile, the blastoderm has been folding
over the germ band from either side, as shown in Fig. 192, and at length
the two folds meet and unite to form two membranes (Fig. 194), namely,
an inner one, or amnion, and an outer one, or serosa.
^O^^^'
Fig. 193. — Transverse section of germ
layers and amnion folds of Clytra. a, am-
nion; e, ectoderm; i, inner layer (meso-
entoderm); s, serosa. — Original, based on
L^caillon's figures.
Fig. 194. — Transverse section of germ
layers and embryonal membranes of Clytra.
a, amnion; ac, amnion cavity; e, ectoderm;
i,- inner layer (meso-entoderm) ; s, serosa. —
After Lecaillon.
Segmentation and Appendages. — On the germ band, which repre-
sents the ventral part of the future insect, the body segments are marked
off by transverse grooves (Figs. 195, 197) ; this segmentation beginning
ii^l^
Fig. 195. — Germ band of a beetle, Lina, in three successive stages. A, unsegmented;
B, with oral segments demarkated; C, with three oral, three thoracic and two abdominal
segments. — After Graber.
usually at the anterior end of the germ band and progressing backward.
Furthermore, an anterior infolding occurs (Fig. 196), forming the stomo-
dceum, from which the mouth, pharynx, oesophagus and other parts of
the fore gut are to arise; a similar but posterior invagination, or procto-
dcBum (Fig. 196), is the beginning, or fundament, of the hind gut.
,'p
132 ENTOMOLOGY
At the anterior end of the germ band is a pair of large procephalic
lobes (Figs. 195, 197), which eventually bear the lateral eyes, and im-
mediately behind these are the
fundaments of the antennas. The
fundaments of the primary paired
appendages are out-pocketings of the
ectodermal germ band, and at first
antennae, mouth parts and legs are
all alike, except in their relative
positions. Behind the antennae (in
Thysanura and Collembola at least)
appears a pair of rudimentary
appendages (Fig. 197, i) which are thought to represent the second
antennae of Crustacea; instead of developing, they disappear in the
embryo or else persist in the adult as mere rudiments. In front of these
5 Fig. 196. — Diagrammatic sagittal sec-
tion of hymenopterous egg to show
stomodffial (s) and proctodaeal (p) in-
vaginations of the germ band (g). —
After Graber.
,aJ.l.ia:-/i
-t2
-pr
Fig. 197. — Ventral aspect of germ
band of a coUembolan, A nurida tnarit-
ima. a, antenna; a^-a", abdominal
appendages; i, intercalary append-
age; I, labrum; U, left labial append-
age; w, mandible; tnx, maxilla; p,
procephalic lobe; pr, proctodaeum;
"-/', thoracic legs.
P-4~~
si I
Fig. 198. — Anterior aspect of embryonal mouth
parts of a coUembolan, Anurida inaritima. a,
antenna ; /, labrum ; Ig, prothoracic leg ; It, left funda-
ment of labium; In, lingua; m, mandible; mx, max-
illa; p, maxillary palpus; si, superlingua.- — After
FOLSOM.
transitory intercalary appendages is the mouth-opening, above which
the labrum and clypeus are already indicated by a single, median
evagination. Behind the mouth the mandibles, maxillae and labium are
DEVELOPMENT
^33
represented by three pairs of fundaments, and in Thysanura and
Collembola a fourth pair is present to form the superlinguae (Fig. 198, si),
already referred to. Next in order are the three pairs of thoracic legs
(Fig. 197) and then, in many cases, paired abdominal appendages (Figs.
197, 199), indicating an ancestral myriopod-like condition; some of these
abdominal Hmbs disappear in the embryo but others develop into abdom-
inal prolegs (Lepidoptera and Tenthre- ^ ^
dinidae), external genital organs (Orthop-
tera, Hymenoptera, etc.) or other structures.
The study of these embryonic fundaments
sheds much light upon the morphology of
the appendages and the subject of segmen-
tation.
Two Types of Germ Bands. — The germ
band described above belongs to the simple
overgrown type, exemplified in Clytra, in
which the germ band retains its original
position and the amnion and serosa arise by
a process of overgrowth (Figs. 193, 194), as
distinguished from the invaginated type,
illustrated in Odonata, in which the germ
band invaginates into the egg, as in Fig.
200, until the ventral surface of the embryo
becomes turned around and faces the dorsal
side of the egg. In this event, a subse-
quent process of revolution occurs, by
means of which the ventral surface of the
embryo resumes its original position (Fig.
201).
Dorsal Closure. — As was said, the germ
band forms the ventral part of the insect.
To complete the general form of the body
the margins of the germ band extend out-
ward and upward (Fig. 202) until they
finally close over to form the dorsal wall of the insect. Besides this
simple method, however, there are several other ways in which the
dorsal closure may be effected.
Nervous System. — Soon after gastrulation, the ventral nervous
system arises as a pair of parallel cords from cells (Fig. 203, n) which
have been derived by direct proliferation from those of the germ band,
Fig. 199. — Embryo of CEcan-
Ihus, ventral aspect, a, antenna;
a^a^, abdominal appendages; e,
end of abdomen; /, labrum; li,
left fundament of labium; Ip,
labial palpus; l^l^, thoracic legs;
m, mandible; mp, maxillary-
palpus; mx, maxilla; p, pro-
cephalic lobe; pr, proctodseum.
— After Ayers.
[34
ENTOMOLOGY
and are therefore ectodermal in origin. This primitive double nerve
cord becomes constricted at intervals into segments, or neuromeres,
which correspond to the segments of the germ band. Each neuromere
Fig. 200.— Diagrammatic sagittal sections to illustrate invagination of germ band in
Calopteryx. a, anterior pole; ac, amnion cavity; am, amnion; b, blastoderm; d, dorsal;
g, germ band; h, head end of germ band; p, posterior pole;
After Brandt.
serosa; v, ventral; y, yolk.-
PiG. 201. — Diagrammatic sagittal sections to illustrate revolution of Calopteryx
embryo, a, antenna; am, amnion; I, labium; l^P, thoracic legs; w, mandible; mx. maxilla;
5, serosa. — After Brandt.
consists of a pair of primitive ganglia, and these are connected together
by paired nerve cords, which later may or may not unite into single
cords; moreover, some of the ganglia finally unite to form compound
ganglia, such as the brain and the sub oesophageal ganglion. In front of
DEVELOPMENT
135
the oesophagus (Fig. 57) are three neuromeres: (i) protocerehrum, which
is to bear the compound eyes; (2) deulocerehrum, or antennal neuromere;
(3) tritocerehrum, which belongs to the segment which bears the rudi-
mentary intercalary appendages spoken of above. Behind the oesopha-
gus are, at most, four neuromeres, namely and in order, mandibular,
superUtigual (found only in Collembola as yet), maxillary and labial.
Fig. 202. — Diagrammatic transverse sections to illustrate formation of dorsal wall in
the beetle, Leptinotarsa. a, amnion (breaking up in C); g, germ band; 5, serosa.— After
Wheeler, from the Journal of Morphology.
Then follow the three thoracic ganglia and ten or eleven abdominal
ganglia. The first three neuromeres always unite to form the brain,
and the next four (always three; but four in Collembola and perhaps
other insects) , to form the suboesophageal gangHon. Compound
ganglia are frequently formed also in the thorax and abdomen by the
union of primitive ganglia.
Tracheae. — The tracheae begin as paired invaginations of the ecto-
derm (Fig. 204, /) ; these simple pockets elongate and unite to form the
main lateral trunks, from
which arise the countless
branches of the tracheal
system.
Mesoderm. — From the
inner layer which was derived
from the germ band by gas-
trulation (Figs. 192-194) are
formed the important germ
layers known as mesoderm and entoderm. Most of the layer becomes
mesoderm, and this splits on either side into chambers, or ccelom
sacs (Fig. 203, c), a pair to each segment. In Orthoptera these
coelom sacs are large and extend into the embryonic appendages, but in
Coleoptera, Lepidoptera and Hymenoptera they are small. These sacs
may share in the formation of the definite body-cavity, though the last
arises independently, from spaces that form between the yolk and the
Pig. 203. — Transverse, section of germ layers
of elytra, c, coelom sac; n, neuroblasts (primi-
tive nervous cells). — After Lecaillon.
i^b
ENTOMOLOGY
mesodermal tissues. From the coelom sacs develop the muscles, fat-
body, dorsal vessel, blood corpuscles, ovaries and testes; the external
sexual organs, however, as well as the vagina and ejaculatory duct, are
ectodermal in origin.
Entoderm. — At its anterior and posterior ends, the inner layer just
referred to gives rise to a mass of cells which are destined to form the
mesenteron, from which the mid intestine develops. One mass is ad-
jacent to the Wind end of the stomodaeal invagination and the other to
that of the proctodaeal in-folding. The two masses become U-shaped
(Fig. 205), and the lateral arms of the two elongate and join so that the
entodermal masses become connected by two lateral strands of cells;
Fig. 204. — Transverse section ot abdomen of Clylra embryo at Fig. 205. — Dia-
an advanced stage of development, a, appendage; e, epithelium of gram of formation
mid intestine; g, ganglion; m, Malpighian tube; mi, muscular layer of entoderm in Lep-
of mid intestine; W5, muscle elements; my, mesenchyme (source of linotarsa. <?, e, ento-
fat-body); s, sexual organ; t, tracheal invagination. — After Lecail- dermal masses; m,
LON. mesoderm. — A f t e r
Wheeler.
by overgrowth and undergrowth from these lateral strands a tube is
formed which is destined to become the stomach, and by the disappear-
ance of the partitions that separate the mesenteron from the stomodaeum
at one end and from the proctodaeum at the other end, the continuity of
the alimentary canal is established. ' The fore and the hind gut, then,
are ectodermal in origin, and the mid gut entodermal.
Polyembryony.— In certain Hymenoptera a single egg may give
rise to many individuals. Thus in some Chalcididae and Proctotrypidae,
according to Marchal, the fertilized ovum segments into many (12-100)
embryos, which develop into as many adults, all the individuals from the
same ovum being of the same sex.
DEVELOPMENT
137
2. External Metamorphosis
Metamorphosis. — One of the most striking phenomena of insect
life is expressed by the term metamorphosis, which means conspicuous
change of form after birth. The egg of a butterfly produces a larva;
this eats and grows and at length becomes a pupa; which, in turn, de-
velops into an imago. These stages are so different (Fig. 28) that with-
out experience one could not know that they pertained to the same
individual.
Holometabola. — The more specialized insects, namely, Coleoptera
(Fig. 206), Strepsiptera, Neuroptera, Mecoptera, Trichoptera, Lepi-
FiG. 206. — Cyllene carya. A, larva; B, pupa; C, imago. X 3.
doptera, Diptera (Figs. 207, 31), Siphonaptera (Fig. 32) and Hymenop-
tera (Fig. 287), undergo this indirect, or complete,^ metamorphosis,
involving profound changes of form and distinguished by the internal
development of the wings and by a pupal stage that is usually inactive,
though active in mosquitoes and some midges, and in certain Neuroptera
just before the transformation. These insects are grouped together as
Holometabola.
Larvae receive such popular names as "caterpillar" (Lepidoptera) ,
''grub" (Coleoptera), and "maggot" (Diptera), while the pupa of a
moth or butterfly (especially the latter) is called a "chrysahs."
'These terms, though somewhat misleading in implication, are currently used.
138
ENTOMOLOGY
Heterometabola. — In a grasshopper, as contrasted with a butterfly,
the imago, or adult, is essentially like the young at birth, except in hav-
ing wings and mature reproductive organs, and the insect is active
throughout Hfe, the wings developing externally; hence the meta-
morphosis is termed direct, or incomplete. This type of transformation,
without a true pupal period, is
characteristic of the more gener-
alized of the metamorphic insects,
namely, Orthoptera, Dermaptera,
Platyptera, Plecoptera (Fig. 19),
Ephemerida (Fig. 20), Odonata
(Fig. 2i),Thysanoptera and Hemi-
ptera (Fig. 208). These orders
constitute the group Heterome-
tabola. Within the limits of the
group, however, various degrees of
metamorphosis occur; thus Plec-
optera, Ephemerida and Odonata
undergo considerable change of
form; a resting, or quiescent, period may precede the imaginal stage,
as in Cicada (Fig. 209). In fact, the various kinds of metamorphosis
Fig
207. — Phormia regina.
puparium; C, imago.
Fig. 208. — Six successive instars of the squash bug, Anasa trislls. x 2.
grade into one another in such a way as to make their classification to
some extent arbitrary and inadequate.
As there is no distinction between larva and pupa in most hetero-
DEVELOPMENT
139
metabolous insects, it is customary to use the term nymph during the
interval between egg and imago.
As a rare abnormality, a holometabolous larva may possess two
pairs of true external wing-pads. This condition has been reported in
Fig. 209. — Cicada libicen. A, imago emerging from nymphal skin; B, the cast skin; C,
imago. Natural size.
several specimens of the meal worm, Tenebrio molitor (by Heymons), six
larvae of the museum beetle, Anthrenus verhasci (A. Busck) and one
pyrochroid larva, Dendroides canadensis (P. B. Powell). In these larvae
Fig. 210. — Eggs of various insects. A, butterfly, Polygonia interrogalionis; B, house
fly, Musca domeslica; C, chalcid, Bruchophagus funebris; D, butterfly, Papilio Iroilus; E,
midge, Dasyneura trifolii; F, hemipteron, Triphleps insidiosus; G, hemipteron, Podisus
maculiventris; H, fly, Drosophila ampelophila. Greatly magnified.
— all coleopterous — it is comparatively an easy step from the internal
wing-rudiment to an external wing-pad, as Dr. W. A. Riley has pointed
out. He regards the phenomenon not as an instance of atavism — a
harking-back to a period when the larva bore wings — but as an example
I40
ENTOMOLOGY
Fig. 211. — Three eggs of the cabbage butter-
fly, Pieris rapa. Greatly magnified, but all
drawn to same scale.
of a kind of premature development (known as prothetaly) in which
characters normally present in the pupal state are present abnormally in
the larva. The latter interpretation is supported by the fact that in
Mr. Powell's specimen, in addition to the larval ocelli, the compound
eyes of the adult are partially
developed, and there are more
antennal segments than in the
normal larva.
Ametabola. — The most gen-
eralized insects, Thysanura and
Collembola, develop to sexual
maturity without a metamor-
phosis; the form at hatching is
retained essentially throughout
life, there are no traces of wings
even in the embryo, and there is no change of habit. These two
orders form the group Ametabola. All other insects have a metamor-
phosis in the broad sense of the term, and are therefore spoken of as
Metahola. In this we follow Packard, rather than Brauer, who uses a
somewhat different set of terms to express the
same ideas.
Stadium and Instar. — During the growth
of every insect, the skin is shed periodically,
and with each molt, or ecdysis, the appearance
of the insect changes more or less. The inter-
vals between the molts are termed stages, or
stadia. ' To designate the insect at any particu-
lar stage, the term instar was proposed and is
much used; thus the insect at hatching is the
first instar, after the first molt the second instar,
and so on.
Eggs. — The eggs of insects are exceedingly
diverse in form. Commonly they are more or
less spherical, oval, or elongate, but there are
innumerable special forms, some of which are
quite fantastic. Something of the variety of
form is shown in Fig. 210. As regards size,
most insect eggs can be distinguished by the naked eye; many of
them tax the vision, however, for example, the elliptical eggs of
Dasyneura leguminicola, which are but .300 mm. in length and .075
Fig. 212. — Chrysopa, laymg
eggs. Slightly enlarged.
DEVELOPMExM I4I
mm. in width; the oval eggs of the cecropia moth, on the other hand,
are as long as 3 mm.
The egg-shell, or chorion, secreted around the ovum by cells of the
ovarian follicle, may be smooth but is usually sculptured, frequently
with ridges which, as in lepidopterous eggs, may serve to strengthen the
shell. The ornamentation of the egg-shell is often exquisitely beautiful,
though the particular patterns displayed are probably of no use, being
mcidentally produced as impressions from the cells which secrete the
chorion. Variations of form, size and pattern are frequent in eggs
of the same species, as appears in Fig. 211.
Always the chorion is penetrated by one or more openings, constitut-
ing the micropyle, for the entrance of spermatozoa.
As a rule, the eggs when laid are accompanied by a fluid of some sort,
which is secreted usually by a cement gland or glands, opening into the
vagina. This fluid commonly serves to fasten the eggs to appropriate
objects, such as food plants, the skin of other insects, the hairs of
mammals, etc.; it may form a pedicel, or stalk, for the egg, as in
Chrysopa (Fig. 2.12); may surround the eggs as a gelatinous envelope,
as in caddis flies, dragon flies, etc. ; or may form a capsule enclosing the
eggs, as in the cockroach.
The number of eggs laid by one female differs greatly in different
species and varies considerably in different individuals of the same
species. Some of the fossorial wasps and bees lay only a dozen or so and
some grasshoppers two or three dozen, while a queen honey bee may lay
a million. Two females of the beetle Prionus laticollis had, respectively,
332 and 597 eggs in the abdomen (Mann). A. A. Girault gives the fol-
lowing numbers of eggs per female, from an examination of twenty egg-
masses of each species:
M.^xiMUM Minimum Average
Thyridopteryx ephememformis {hdigwoxm) 1649 465 941
Malacosoma americana (tent caterpillar) 466 313 375-5
Chionas pis furf lira (scurfy scale) 84 33 66.5
Hatching. — Many larvae, caterpillars for example, simply eat their
way out of the egg-shell. Some maggots rupture the shell by contor-
tions'of the body. Some larvae have special organs for opening the
shell; thus the grub of the Colorado potato beetle has three pairs of
hatching spines on its body (Wheeler) and the larval flea has on its head
a temporary knife-like egg-opener (Packard). The process of hatching
varies greatly according to the species, but has received very little
attention.
142
ENTOMOLOGY
Larva. — Although larvae, generally speaking, differ from one another
much less than their imagines do, they are easily referable to their orders
and usually present specific differences. Larvae that display individual
adaptive characters of a positive kind (Lepidoptera, for example) are
easy to place, but larvae with negative adaptive characters (many Dip-
tera and Hymenoptera) are often hard to identify.
Thysanuriform Larvae. — Two types of larvae have been recognized
by Brauer, Packard and other authorities: thysanuriform and eruciform;
respectively generahzed and specialized in their organization. The
former term is applied to many larvae and nymphs (Fig. 213, C) on
Fig. 213. — Types of larvae. A, B, Thysanura; C, thysanuriform nymph; E-I, cruci-
form larvae. A, Campodea; B, Lepisma; C, perlid nymph (Plecoptera) ; D, Libellula (Odo-
nata); E, Tenlhredopsis (Hymenoptera); F, Lachnosterna (Coleoptera); G, Melanotus
(Coleoptera); H, Bombiis (Hymenoptera); /, Hypoderma (Diptera).
account of their resemblance to Thysanura, of which Campodea and
Lepisma are types. The resemblance lies chiefly in the flattened form,
long body, hard plates, long legs and antennae, caudal cerci, well-
developed mandibulate mouth parts, and active habits, with the accom-
panying sensory specializations. These characteristics are permanent
in Thysanura, but only temporary in metamorphic insects, and their
occurrence in the latter forms may properly be taken to indicate that
these insects have been derived from ancestors which were much like
Thysanura.
Thysanuriform characters are most pronounced in nymphs of Blat-
tidae, Forficulidae, Perlidae and Ephemeridae, but occur also in the larvae
of some Neuroptera (Mantispa) and Coleoptera (Carabidae and Meloi-
dae). These primitive characters are gradually overpowered, in the
course of larval evolution, by secondary, or adaptive features.
DEVELOPMENT
f43
Eruciform Larvae. — The prevalent type of larva among holometab-
olous ipsects is the eruciform (Fig. 213, E-I), illustrated by a caterpillar
or a maggot. Here the body is cylindrical and often fleshy; the integ-
ument weak; the legs, antennae, cerci, and mouth parts reduced, often
to disappearance; the habits sedentary and the sense organs corre-
spondingly reduced. These characteristics are interpreted as being
results of partial or entire disuse, the amount of reduction being pro-
portional to the degree of inactivity. Extreme reduction is seen in the
maggots of parasitic and such other Diptera as, securing their food with
almost no exertion, are simple in form, thin-skinned, legless, with only
a mere vestige of a head and with sensory powers of but the simplest
kind.
Transitional Forms. — The eruciform is clearly derived from the
Fig. 214. — Mantispa. A, larva at hatching — thysanuriform; B, same larva just before
first molt — now becoming eruciform. C, imago, the wings omitted; D, winged imago,
slightly enlarged. — A and B after Brauer; C and D after Emerton, from Packard's Text-
Book of Entomology, by permission of the Macmillan Co.
thysanuriform type, as Brauer and Packard have shown, the continuity
between the two types being established by means of a complete series
of intermediate stages. The beginning of the eruciform type is found
in Neuroptera, where the campodeoid sialid larva assumes a quiescent
pupal condition. The key to the origin of the complete metamorpho-
sis, involving the eruciform condition, Packard finds in the neuropterous
genus Mantispa (Fig. 214), the first larva of which is truly campodei-
form and active. Beginning a sedentary life, however, in the egg-sac of
a spider, it loses the use of its legs and the antennae become partly
aborted, before the first molt. In Packard's words, "Owing to this
change of habits and surroundings from those of its active ancestors, it
144 ENTOMOLOGY
changes its form, and the fully grown larva becomes cylindrical, with
small slender legs, and, owing to the partial disuse of its jaws, acquires
a small, round head." Meloidae (Fig. 220) afford other excellent
examples of the transition from the thysanuriform to the cruciform
condition during the life of the individual.
Thysanuriform characters become gradually suppressed in favor of
the cruciform, until, in most of the highly developed orders (Mecoptera,
Trichoptera, Lepidoptera, Diptera, Siphonaptera and Hymenoptera),
they cease to appear, except for a few embryonic traces— an illustration
of the principle of ''acceleration in development."
Growth. — The larval period is pre-eminently one of growth. In
Heterometabola, growth is continuous during the nymphal stage, but
in Holometabola this important function becomes relegated to the larval
stage, and pupal development takes place at the expense of a reserve
supply of food accumulated by the larva.
The rapidity of larval growth is remarkable. Trouvelot found that
the caterpillar of Telea polyphemus attains in 56 days 4,140 times its
original weight (|^o grain), and has eaten an amount of food 86,000
times its primitive weight. Other larvae exceed even these figures; thus
the maggot of a common flesh fly attains 200 times its original weight
in 24 hours.
Ecdysis. — The exoskeleton, unfitted for accommodating itself to the
growth of the insect, is periodically shed, and along with it go not only
such integumentary structures as hairs and scales, but also the chitinous
lining, or intima, of the stombdaeum, proctodaeum, tracheae, integumen-
tary glands, etc. The process of molting, or ecdysis, in caterpillars is
briefly as follows. The old skin becomes detached from the body by an
intervening fluid of hypodermal origin; the skin dries, shrinks, is pushed
backward by the contractions of the larva, and at length splits near the
head, frequently under the neck ; through this split appear the new head
and thorax, and the old skin is worked back toward the tail until the
larva is freed of its exuvice. The details of the process are, however, by
no means simple. Ecdysis is probably something besides a provision
for growth, for Collembola continue to molt long after growth has
ceased, and the winged May fly sheds its skin once after emergence.
The meaning of this is not known, though ecdysis has an excretory
importance in the case of Collembola, which are exceptional among
insects in having no Malpighian tubes.
Number of Molts. — The frequency of molting differs greatly in
different orders of insects. Locustidae (formerly " Acridiidae ") have
DEVELOPMENT 1 45
five molts; many Heteroptera, as the chinch bug and squash bug, have
five (with six instars) ; the periodical cicada, six (Marlatt) ; the larva of
the Colorado potato beetle, three; Lepidoptera usually four or five, but
often more, as in Isia Isabella, which molts as many as ten times (Dyar) ;
the house fly, Musca domestica, two molts (three larval instars) . Pack-
ard suggests that cold and lack of food during hibernation in arctians
(as I. Isabella) and partial starvation in the case of some beetles, cause
a great number of molts by preventing growth, the hypodermis cells
meanwhile retaining their activity.
The appearance of the insect often changes greatly with each molt,
particularly in caterpillars, in which the changes of coloration and
armature may have some phylogenetic significance, as Weismann has
attempted to show in the case of sphingid larvae.
Adaptations of Larvae. — Larvae exhibit, innumerable conformities
of structure to environment. The greatest variety of adaptive struc-
tures occurs in the most active larvae, such as predaceous forms, ter-
restrial or aquatic. These have well-developed sense organs, excellent
powers of locomotion, special protective and aggressive devices, etc.
In insects as a whole, the environment of the larva or nymph and that
of the adult may be very different, as in the butterfly or the dragon fly,
and the larvae are modified in a thousand ways for their own immediate
advantage, without any direct reference to the needs of the imago.
The chief purpose, so to speak, of the larva is to feed and grow, and
the largest modifications of the larva depend upon nutrition. Take as
one extreme, the legless, headless, fleshy and sluggish maggot, embedded
in an abundance of food, and as the other extreme the active and
''wide-awake" larva of a carabid beetle, dependent for food upon its
own powers of sensation, locomotion, prehension, etc., and obHged
meanwhile to protect or defend itself. Between these extremes come
such forms as caterpillars, active to a moderate degree. The great
majority of larval characters, indeed, are correlated with food habits,
directly or indirectly; directly in the case of the mouth parts, sensory
and locomotor organs, and special structures for obtaining special food;
indirectly, as in respiratory adaptations and protective structures,
these latter being numerous and varied.
Larvae that live in concealment, as those that burrow in the ground
or in plants, have few if any special protective structures; active larvae,
as those of Carabidae, have an armor-like integument, but owe their
protection from enemies chiefly to their powers of locomotion and their
aversion to Hght (negative phototro pism) ; various aquatic nymphs {Z ait ha,
146 ENTOMOLOGY
Odonata) are often coated with mud and therefore difficult to distin-
guish so long as they do not move; caddis worms are concealed in their
cases, and caterpillars are often sheltered in a leafy nest. There is no
reason to suppose that insects conceal themselves consciously, however,
and one is not warranted in speaking of an instinct for concealment in the
case of insects — since everything goes to show that the propensity to
hide, though advantageous indeed, is simply a reflex, inevitable, nega-
tive reaction to light (negative phototropism) or a positive reaction to
contact {positive thigmotropism).
Exposed, sedentary larvae, as those of many Lepidoptera and Cole-
optera, often exhibit highly developed protective adaptations. Cater-
pillars may be colored to match their surroundings and may resemble
twigs, bird-dung, etc.; or larvae may possess a disagreeable taste or
repellent fluids or spines, these odious qualities being frequently
associated with warning colors.
Larvae need protection also against adverse climatal conditions,
especially low temperature and excessive moisture. The thick hairy
clothing of some hibernating caterpillars, as Isia isabella, doubtless
serves to mollify sudden changes of temperature. Naked cutworms
hibernate in well-sheltered situations, and the grubs of the common
"May beetles," or "June bugs," burrow down into the ground below
the reach of frost. Ordinary high temperatures have little effect upon
larvae, except to accelerate their growth. Excessive moisture is fatal
to immature insects in general — conspicuously fatal to the chinch bug,
Rocky Mountain locust, aphids and sawfly larvae. The effect of mois-
ture may be an indirect one, however; thus moisture may favor the
development of bacteria and fungi, or a heavy rain may be disastrous
not only by drowning larvae, but also by washing them off their food
plants.
As a result of secondary adaptive modifications, larvae may differ
far more than their imagines. Thus Platygaster in its extraordinary first
larval form (Fig. 221) is entirely unlike the larvae of other parasitic
Hymenoptera, reminding one, indeed, of the crustacean Cyclops rather
than the larva of an insect. As Lubbock has said, the characters of a
larva depend (i) upon the group of insects to which the larva belongs
and (2) upon the special environment of the larva.
Pupa. — The term pupa is strictly applicable to holometabolous
insects only. Most Lepidoptera and many Diptera have an obtect
pupa (Fig. 215), or one in which the appendages and body are compactly
united; as distinguished from the free pupa of Neuroptera, Trichoptera,
DEVELOPMENT
147
Coleoptera and others, in which the appendages are free (Fig. 206);
but this distinction cannot always be drawn sharply. Diptera present
also the coarctate type of pupa (Fig. 207), in which the pupa remains
enclosed in the old larval skin, or puparium.
Pupal characters, though doubtless of great adaptive and phylogene-
tic significance, have received but little attention. Lepidopterous pupae
present many puzzling characters, for example, an eye-like structure
(Fig. 216) suggesting an ancestral active condition, such as still occurs
among heterometabolous insects.
Fig. 215. — Obtect
pupa of milkweed but-
terfly, Anosia plexip-
pus, natural size.
Pig. 216. — Head
of chrysalis of Pa-
pilio polyxenes, to
show eye-like struc-
ture. Enlarged.
Pupation of a Caterpillar.— The process of pupation in a caterpillar
has been carefully observed by Riley. The caterpillar of the milkweed
butterfly (PI. I, ^) spins a mass of silk in which it entangles its suranal
plate and anal prolegs and then hangs downward, bending up the ante-
rior part of the body (B) , which gradually becomes swollen. The skin of
the caterpillar splits dorsally from the head backward, and is worked
back toward the tail (C and D) by the contortions of the larva.
The way in which the pupa becomes attached to its silken support
is rather complex. Briefly, while the larval skin still retains its hold on
the support, the posterior end of the pupa is withdrawn from the old
integument while the latter is being temporarily gripped between two
of the abdominal segments of the pupa, and by the vigorous whirling
and twisting of the body the hooks of the terminal cremaster of the pupa
are entangled in the silken support. At first the pupa is elongate (£)
and soft, but in an hour or so it has contracted, hardened, and assumed
its characteristic form and coloration (F).
Pupal Respiration. — Except under special conditions, pupse breathe
by means of ordinary abdominal spiracles. Aquatic pupae have special
148 ^ ENTOMOLOGY
respiratory organs, such as the tracheal fi.\a.ments of Si mulium (Fig. 233),
and the respiratory tubes of Culex (Fig. 232).
Pupal Protection. — Inactive and helpless, most pupae are concealed
in one way or another from the observation of enemies and are pro-
tected from moisture, sudden changes of temperature, mechanical shock
and other adverse influences. The larvae of many moths burrow into
the ground and make an earthen cell in which to
pupate; a large number of coleopterous larvae {Lach-
A nosterna, Osmoderma, Passalus, Lucanus, etc.) make
^^ a chamber in earth or wood, the walls of the cells
^^m being strengthened with a cementing fluid or more or
^~"'-J less silk, forming a rude cocoon. Silken cocoons are
fljjB spun by some Neuroptera (Chrysopidae, Fig. 217),.
^Hv by Trichoptera (whose cases are essentially cocoons),
^Mf Lepidoptera, a few Coleoptera (as Curculionidae,
^ Donacia) , some Diptera (as Itonididae) , Siphonaptera,
and many Hymenoptera (for example, Tenthredi-
^^'^- 217— Co- nidae, Ichneumonidae, wasps, bees and some ants).
coon of Chrysopa, . .
after emergence of The cocoon-making instinct is most highly devel-
largf d. ^^ ^ ^ ^^" oped in Lepidoptera and the most elaborate cocoons
are those of Saturniidae. The cocoon of Samia
cecropia is a tough, water-proof structure and is double (Fig. 218),
there being two air spaces around the pupa; thus the pupa is pro-
tected against moisture and sudden changes of temperature and from
most birds as well, though the downy woodpecker not infrequently punc-
tures the cocoon. S. cecropia binds its cocoon firmly to a twig ; Tropcea
luna and Telea polyphemus spin among leaves, and their cocoons (with
some exceptions) fall to the ground; Callosamia promethea, whose cocoon
is covered with a curved leaf, fastens the leaf to the twig with a wrapping
of silk, so that the leaf with its burden hangs to the twig throughout the
winter. The leaves surrounding cocoons may render them inconspicu-
ous or may serve merely as a foundation for the cocoon. While silk and
often a waterproof gum or cement form the basis of a cocoon, much
foreign material, such as bits of soil or wood, is often mixed in; the
cocoons of many common Arctiidae, as Diacrisia virginica and Isia
Isabella, consist principally of hairs, stripped from the body of the
larva.
Butterflies have discarded the cocoon, traces of which occur in
Hesperiidae, which draw together a few leaves with a scanty supply of
silk to make a flimsy substitute for a cocoon. Papilionid and pierid
Successive stages in the pupation of the milkweed caterpillar, Anosia plexippus. Natural
size.
DEVELOPMENT 15I
pupae are supported by a silken girdle (Fig. 29), and nymphalid chrysa-
lides hang freely suspended by the tail (Fig. 215).
Cocoon-Spinning. — The caterpillar af Telea polyphemus "feels with
its head in all directions, to discover any leaves to which to attach the
fibres that are to give form to the cocoon. If it finds the place suitable,
it begins to wind a layer of silk around a twig, then a fibre is attached to
a leaf near by, and by many times doubling this fibre and making it
shorter every time, the leaf is made to approach the twig at the distance
necessary to build the cocoon; two or three leaves are disposed like this
one and then the fibres are spread between them in all directions, and
soon the ovoid form of the cocoon distinctly appears. This seems to
Fig.
-Cocoon of Samia cecropia, cut open to show the two silken layers and the
enclosed pupa. Natural size.
be the most difiicult feat for the worm to accompHsh, as after this the
work is simply mechanical, the cocoon being made of regular layers
of silk united by a gummy substance. The silk is distributed in
zigzag lines about one-eighth of an inch long. When the cocoon is
made, the worm will have moved his head to and fro, in order to distrib-
ute the silk, about two hundred and fifty-four thousand times. After
about half a day's work, the cocoon is so far completed that the worm
can hardly be distinguished through the fine texture of the wall; then
a gummy resinous substance, sometimes of a light brown color, is spread
over all the inside of the cocoon. The larva continues to work for four
or five days, hardly taking a few minutes of rest, and finally another
coating is spun in the interior, when the cocoon is all finished and com-
pletely air tight. The fibre diminishes in thickness as the completion
of the cocoon advances, so that the last internal coating is not half so
thick and so strong as the outside ones." (Trouvelot.)
152 ENTOMOLOGY
Emergence of Pupa. — Subterranean pupae wriggle their way to
the surface of the ground, often by the aid of spines (Fig. 219), that
catch successively into the surrounding soil. These locomotor spines
may occur on almost any part of the pupa, but occur commonly on the
abdominal segments, as in lepidopterous pupae; the
t extremity of the abdomen, also, bears frequently
one or more spinous projections, as in TipuHdae,
Carabidae and Lepidoptera, to assist the escape of
the pupa. These structures are found also in pupae,
as those of Sesiidae, that force their way out of the
stems of plants in which the larvae have lived. The
emergence from the cocoon is accomplished in some
• cases by the pupa, in others by the imago. Hemero-
^ biidae, Trichoptera and the primitive lepidopteron
Fig. 219.— Sub- Eriocephala use the pupal mandibles to cut an open-
terranean pupa of _ _ -^ ^ _ ^ ^
Anisoia. Enlarged, ing in the cocoou; whilc many lepidopterous pupae
have on the head a beak for piercing the cocoon, or
teeth for rending or cutting the silk.
Eclosion. — During the last few hours before the emergence of a
butterfly the colors of the imago develop and may be seen through the
transparent skin of the chrysalis (PI. 11 A). No movement occurs, how^-
eyer, until several seconds before emergence; then, after a few convul-
sive movements of the legs and thorax of the imprisoned insect, the
pupa skin breaks in the region of the tongue and legs {B), a secondary
split often occurs at the back of the thorax, and the butterfly emerges
iC~E) with moist body, elongated abdomen and miniature wings.
Hanging to the empty pupa case (F), or to some other available sup-
port, the insect dries and its wings gradually expand (G, H) through the
pressure of the blood. At regular intervals the abdomen contracts
and the wings fan the air, and sooner or later a drop or two of a dull
greenish fluid (the meconium) is emitted from the alimentary canal.
The expansion of the wings takes place rapidly, and in less than an
hour, as a rule, they have attained their full size (/).
T. polyphemus is "provided with two glands opening into the mouth,
which secrete during the last few days of the pupa state, a fluid which is
a dissolvent for the gum so firmly uniting the fibres of the cocoon. This
liquid is composed in great part of bombycic acid. When the insect has
accomplished the work of transformation which is going on under the
pupa skin, it manifests a great activity, and soon the chrysahs covering
bursts open longitudinally upon the thorax; the head and legs are soon
Successive stages in the emergence of the milkweed butterfly, Anosia plexippus, from the
chrysalis. Natural size.
DEVELOPMENT 1 55
disengaged, and the acid fluid flows from its mouth, wetting the inside of
the cocoon. The process of exclusion from the cocoon lasts for as much
as half an hour. The insect seems to be instinctively aware [?] that
some time is required to dissolve the gum, as it does not make any at-
tempt to open the fibres, and seems to wait with patience this event.
When the liquid has fully penetrated the cocoon, the pupa contracts its
body, and pressing the hinder end, which is furnished with little hooks,
against the inside of the cocoon, forcibly extends its body; at the same
time the head pushes hard upon the fibres and a little swelling is
observed on the outside. These contractions and extensions of the
body are repeated many times, and more fluid is added to soften the
gum, until under these efforts the cocoon swells, and finally the fibres
separate, and out comes the head of the moth. In an instant the legs
are thrust out, and then the whole body appears; not a fibre has been
broken, they have only been separated.
"To observe these phenomena, I had cut open with a razor a small
portion of a cocoon in which was a living chrysalis nearly ready to trans-
form. The opening made was covered with a piece of mica, of the same
shape as the aperture, and fixed to the cocoon with mastic so as to make
it solid and air-tight; through the transparent mica I could see the move-
ments of the chrysalis perfectly well.
''When the insect is out of the cocoon, it immediately seeks for a
suitable place to attach its claws, so that the wings may hang down, and
by their own weight aid the action of the fluids in developing and
unfolding the very short and small pad-like wings. Every part of the
insect on leaving the cocoon, is perfect and with the form and size of
maturity, except the pad-like wings and swollen and elongated abdomen,
which still gives the insect a worm-like appearance; the abdomen con-
tains the fluids which flow to the wings.
"When the still immature moth has found a suitable place, it re-
mains quiet for a few minutes, and then the wings are seen to grow very
rapidly by the afiiux of the fluid from the abdomen. In about twenty
minutes the wings attain their full size, but they are still like a piece of
wet cloth, without consistency and firmness, and as yet entirely unfit for
flight, but after one or two hours they become sufficiently stiff, assuming
the beautiful form characteristic of the species" (Trouvelot). The
expansion of the wing is due to blood-pressure brought about chiefly by
the abdominal muscles. In the freshly-emerged insect, the two mem-
branes of the wing are corrugated, and expansion consists in the flatten-
ing out of these folds. The wing is a sac, which would tend to enlarge
150 ENTOMOLOGY
into a balloon-shaped bag, were it not for hypodermal fibres which hold
the wing-membranes closely together (Mayer). Tropcea luna and
Philosamia cynthia cut and force an opening through the cocoon by
means of a pair of saw-like organs, one at the base of each front wing.
The cocoons of Samia cecropia and Callosamia promethea do not
have a gummy coating over the entire interior. In each case the end
through which the moth emerges is composed of silken fibres loosely
pulled together and not covered with a gummy substance. It is as if
each layer of the cocoon was spun into a fringe at this end, the fringes
of all layers being bunched together forming a Httle cone. Jn the co-
coon of Samia cecropia, it is possible to push a pencil through this
fringe with apparently no effort. The fibres part readily, it being neces-
sary to break only a few in the extreme outside layer. The same can
be said of the cocoon of C. promethea (H. B. Weiss).
The temperature inside a cocoon is practically the same as that of the
surrounding air, there being a constant tendency for the inside tem-
perature to approach that of its surroundings. Sudden changes of
temperature do not occur within a cocoon. When the outside tem-
perature is suddenly lowered, as from io° C to o° C, the temperature in
a cocoon falls gradually, and even during a gradual rise the cocoon-
temperature lags behind that of its surroundings, on account of the poor
conducting qualities of air and silk (H. B. Weiss).
Hypermetamorphosis. — In a few remarkable instances, metamor-
phosis involves more than three stages, owing to the existence of super-
numerary larval forms. This phenomenon of hypermetamorphosis
occurs notably in the coleopterous genera Melo'e, Epicauta, Sitaris
and Rhipiphorus, in Strepsiptera and in several parasitic Hymenoptera.
In the oil-beetle, Melo'e, as described by Riley, the newly-hatched
larva {triungulin) is active and campodea-form. It climbs upon a
flower and thence upon the body of a bee {Anthophora) , which carries
it to the nest, where it eats the egg of the bee. After a molt, the larva
though still six-legged, has become cylindrical, fleshy and less active,
resembling a lamellicorn larva; it now appropriates the honey of the bee.
With plenty of rich food at hand the larva becomes sluggish, and after
another molt appears as a pseudo-pupa, with functionless mouth
parts and atrophied legs. From this pseudo-pupa emerges a third
larval form, of the pure cruciform type, fat and apodous like the bee-
larvae themselves. After these four distinct stages the larva becomes
a pupa and then a beetle.
Epicauta, another meloid, has a similar history. The triungulin
DEVELOPMENT
:57
(Fig. 220, A) of E. vittata burrows into an egg-pod of Melanoplus differ-
entialis and eats the eggs of that grasshopper. After a molt the second
larva {carabidoid form) appears; this (B) is soft, with reduced legs and
mouth parts and less active than the triungulin. A second molt and
the scarabceidoid form of the second larva is assumed; the legs and mouth
parts are now rudimentary and the body more compact than before.
A third and a fourth molt occur with little change in the form of the
second larva, which is now in its ultimate stage (C) . After the fifth
molt, however, the coarctate larva, or pseudo-pupa, appears; this {D)
hibernates and in spring sheds its skin and becomes the third larva,
Fig. 220. — Stages in the hypermetamorphosis of Epicauta. A, triungulin; B, carabi-
doid stage of second larva; C, ultimate stage of second larva; D, coarctate larva; E, pupa; F,
imago. E is species cinerea; the others are viltata. All enlarged except F. — After Riley,
from Trans. St. Louis Acad. Science.
which soon transforms to a true pupa (£), from which the beetle (F)
shortly emerges. Thus the pupal stage is preceded by at least three
distinct larval stages.
Strepsiptera, the subject of two important volumes by Dr. W. D.
Pierce, are all hypermetamorphic. These parasites affect almost
exclusively Hymenoptera and Homoptera, causing the "stylopized"
condition known to collectors of bees, wasps or bugs, in which the pres-
ence of the parasite is indicated by a flat disk-like plate (in the female
parasite) or a tuberculate rounded projection (male) protruding from
between segments of the abdomen. The male is winged but the female
is maggot-like and sedentary, a mere sac of eggs, often two thousand
or more in number, which hatch inside the body of the mother into active
little hexapodous thysanuriform larvae known as triiingulinids . These
158
ENTOMOLOGY
are probably carried by the host to flowers or other places where they
are able to attach themselves to the bodies of their future hosts. After
penetrating into the body of the host the larva grows rapidly ; with the
first molt the eyes and legs are lost, the second instar being scarabae-
idoid in form; after the second molt the male and female larvae differ
in development.
The most extraordinary metamorphoses have been found among
parasitic Hymenoptera, as in Platygaster, a proctotrypid which infests
the larva of Cecidomyia. The egg of Platygaster, according to Ganin,
Pig. 221. — Stages in the hypermetamorphosis of Platygaster. A, first larva; B, second
larva; C, third larva; a, antenna; h, brain;/, fat-tissue; h, hind intestine; m, mandible; mo,
mouth; ms, muscle; w, nerve cord; r, reproductive organ of one side; s, salivary gland; t,
trachea. — After Ganin.
hatches into a larva of bizarre form (Fig. 221, A), suggesting the crusta-
cean Cyclops, rather than an insect. This first larva has a blind food
canal and no nervous, circulatory or respiratory systems. After a
molt the outHneis oval {B), and there are no appendages as yet, though
the nervous system is partially developed. Another molt, and the
third larva appears (C), elHptical in contour, externally segmented, with
tracheae and a pair of mandibles. From now on, the development is
essentially like that of other parasitic Hymenoptera.
Equally anomalous are the changes undergone by Polynema, a proc-
totrypid parasite in the eggs of dragon flies, and by the proctotrypid
Teleas, which affects the eggs of the tree cricket {(Ecanthus). In all
these cases the larvae go through changes which in most other insects are
confined to the egg stage. In other words, the larva hatches before its
embryonic development is completed, so to speak.
DEVELOPMENT 159
Significance of Metamorphosis. — "The essential features of meta-
morphosis," says Sharp, "appear to be the separation in time of growth
and development and the limitation of the reproductive processes to a
short period at the end of the individual life."
The simplest insects, Thysanura, have no metamorphosis, and show
no traces of ever having had one. Hence it is inferred that the first
insects had none; in other words, the phenomenon of metamorphosis
originated later than insects themselves. Successive stages in the
evolution of metamorphosis are illustrated in the various orders of
insects.
The distinctive mark of the simplest metamorphosis, as in Orthop-
tera and Hemiptera, is the acquisition of wings; growth and sexual
development proceeding essentially as in the non-metamorphic insects
(Thysanura and Collembola) . Here the development of wings does not
interfere with the activity of the insect; its food habits remain unaltered;
throughout life the environment of the individual is practically the same.
Even when considerable difference exists between the nymphal and
imaginal environments, as in Ephemerida and Odonata, the activity of
the individual may still be continuous, even if somewhat lessened as the
period of transformation approaches.
With Neuroptera, the pupal stage appears. In these and all other
holometabolous insects the larva accumulates a surplus of nutriment
sufficient for the further development, which becomes condensed into
a single pupal stage, during which external activity ceases temporarily.
With the increasing contrast between the organization of the larva
and that of the imago, the pupal stage gradually becomes a necessity.
Metamorphosis now means more than the mere acquisition of wings, for
the larva and the imago have become adapted to widely different en-
vironments, chiefly as regards food. The caterpillar has biting mouth
parts for eating leaves, while the adult has sucking organs for obtaining
liquid nourishment; the maggot, surrounded by food that may be ob-
tained almost without exertion, has but minimum sensory and locomotor
powers and for mouth parts only a pair of simple jaws; as contrasted
with the fly, which has wings, highly developed mouth parts and sense
organs, and many other adaptations for an environment which is
strikingly unKke that of the larva; so also in the case of the higher
Hymenoptera, where maternal or family care is responsible for the help-
less condition of the larva.
Thus it is evident that the change from larval to imaginal adapta-
tions is no longer congruous with continuous external activity; a quies-
l6o ENTOMOLOGY
cent period of reconstruction becomes inevitable (though this statement
does not, of course, explain anything).
As was. said, the cruciform type of larva has been derived from the
thysanuriform type, the strongest evidence of this being the fact that
among hypermetamorphic insects, the change from the one to the other
takes place during the lifetime of the individual. Furthermore, the
cruciform condition is plainly an adaptive one, brought about by an
abundant and easily obtainable supply of food. The lack of a thysanuri-
form stage in the development of the most specialized cruciform larvae,
as those of flies and bees, is regarded by Hyatt and Arms as an illustra-
tion of the general principle known as "acceleration of development,"
according to which newer and useful adaptive characters tend to appear
earlier and earlier in the development, gradually crowding upon and
forcing out older and useless characters. In connection with this sub-
ject, the appearance of temporary abdominal legs in embryo bees is
significant, as indicating an ancestral active condition. In accounting
for the evolution of metamorphosis, the theory of natural selection finds
one of its most important applications.
3. Internal Metamorphoses
In Heterometabola, the internal post-embryonic changes are as di-
rect as the external changes of form; in Holometabola, on the contrary,
not all the larval organs pass directly into imaginal organs, for certain
larval tissues are demolished and their substance reconstructed into
imaginal tissues. When indirect, the internal metamorphosis is
nevertheless continuous and gradual, without the abruptness that
characterizes the external transformation. In the larval stage imaginal
organs arise and grow; in the pupal stage the purely larval organs
gradually disappear while the imaginal organs are continuing their
development.
Phagocytes.^The destruction of larval tissues, or histolysis, is due
often to the amoeboid blood corpuscles, known as leucocytes or phago-
cytes, which attack some tissues and absorb their material, but later
are themselves food for the developing imaginal tissues. The construc-
tion of tissues is termed histogenesis.
In Coleoptera the degeneration of the larval muscles is entirely
chemical, there being no evidence of phagocytosis, according to Dr.
R. S. Breed. Berlese, indeed, goes so far as to deny in general the
destructive action of leucocytes on larval tissues.
DEVELOPMENT
l6l
Imaginal Buds. — The wings and legs of a fly originate in the larva
in the form of cellular masses, termed imaginal buds, or histoblasts, as
Weismann discovered. Thus in the larva of Corethra, there are in
each thoracic segment a pair of dorsal buds and a pair of ventral buds
(Fig. 222), each bud being clearly an evagination of the hypodermis
at the bottom of a previous invagination. The six ventral buds form
the legs eventually; of the dorsal buds, the middle and posterior pairs
form, respectively, the wings and the halteres, and the anterior pair
Fig. 222. — Diagram-
matic transverse section of
Corethra larva, to show
imaginal buds of wings (w)
and legs (I); h, hypoder-
mis; i, integument. — Modi-
fied from Lang's Lehrbuch.
C D
Pig. 223. — Diagrammatic t-ransverse sections of muscid
larvae, to show imaginal buds, h, larval hypodermis; i, larval
integument; ih, imaginal hypodermis; I, imaginal bud of leg;
w, imaginal bud of wing. — Modified from Lang's Lehrbuch.
form the pupal respiratory processes. Each imaginal bud is situated in
a peripodal cavity, the wall of which (peripodal membrane) is continu-
ous with the general hypodermis; as the legs and wings develop, they
emerge from their peripodal sacs and become free.
In Corethra but little histolysis occurs, most of the larval structures
passing directly into the corresponding structures of the adult. Core-
thra is, indeed, in many respects intermediate between heterometabo-
lous and holometabolous insects as regards its internal changes.
Muscidae. — In Muscidae, as compared with Corethra, the imaginal
buds are more deeply situated, the peripodal membrane forming a
l62
ENTOMOLOGY
stalk (Fig. 223), and the processes of histolysis and histogenesis become
extremely complicated. The hypodermis, muscles, alimentary canal
and fat-body are gradually broken down and remodeled, and part of
the respiratory system is reorganized, though the dorsal vessel and the
central nervous system, uninterrupted in
their functions, undergo comparatively
little alteration.
The imaginal hypodermis of the tho-
rax arises from thickenings of the peri-
podal membrane which spread over the
larval hypodermis, while the latter is
gradually being broken down by the
leucocytes; in the head and abdomen
the process is essentially the same as in
the thorax, the new hypodermis arising
from imaginal buds.
Most of the larval muscles, excepting
the three pairs of respiratory muscles,
undergo dissolution. The imaginal
muscles have been traced back to meso-
dermal cells such as are always associated
with imaginal buds.
Hymenoptera and Lepidoptera. —
The internal transformation in Hymen-
optera, according to Bugnion, is less pro-
found than in Muscidae and more exten-
sive than in Coleoptera and Lepidoptera.
The internal metamorphosis in Lepidop-
tera resembles in many respects that of
Corethra. In both these orders the dorsal
pair of prothoracic buds is absent. In
a full-grown caterpillar the fundaments of the imaginal legs and
wings (Fig. 224) may be seen, the wings in a frontal section of the
larva appearing as in Fig. 225. Many of the details of the internal
metamorphosis in Lepidoptera have been described by Newport and
Gonin. Figure 226, after Newport, shows some of the more evi-
dent internal differences in the larva, pupa and imago of a lepidop-
terous insect.
Significance of Pupal Stage. — To repeat — among holometabolous
insects the function of nutrition becomes relegated to the larval stage
Pig. 224. — Imaginal buds of full
grown larva of Pieris, dorsal aspect.
b, brain; m, mid intestine; s^, pro-
thoracic spiracle; s*, first abdominal
spiracle; sg, silk gland; /, pro-
thoracic bud; II, bud of fore wing;
III, bud of hind wing. — After
Gonin.
DEVELOPMENT
163
"^iSsiuiuiin^j^
Fig. 225. — Section through left hind wing in larva of Pieris rapce, the section being a
frontal one of the caterpillar; the base of the wing is anterior in position, and the apex
posterior, c, cuticula; //, hypodermis; t, trachea; w, developing wing. — After Mayer.
Pig. 226. — Internal transformations of Sphinx ligustri. A, larva; B, pupa; C, moth;
a, aorta; an, antenna; b, brain; /, fore intestine; fr, food reservoir; h, hind intestine; ht,
heart; tn, mid intestine; mt, Malpighian tubes; p. proboscis; s, suboesophageal ganglion;
t, testis; tg, thoracic ganglia; v, ventral nerve cord. — After Newport.
I 64 ENTOMOLOGY
and that of reproduction to the imaginal stage. Larva and imago
become adapted to widely different environments. So dissimilar
are the two environments that a gradual change from the one to the
other is no longer possible; the revolutionary changes in structure
necessitate a temporary cessation of external activity.
CHAPTER IV
ADAPTATIONS OF AQUATIC INSECTS
Ease, versatility and perfection of adaptation are beautifully exem-
plified in aquatic insects.
Systematic Position. — Aquatic insects do not form a separate group
in the system of classification, but are distributed among several orders,
of which Plecoptera, Ephemerida, Odonata and Trichoptera are pre-
eminently aquatic. One third of the families of Heteroptera and less
than one fourth those of Diptera are more or less aquatic. One tenth
of the famihes of Coleoptera frequent the water at one stage or another,
two famihes of Neuroptera, and only half a dozen genera of Lepidoptera.
A few Collembola live upon the surface of water; and several Hymenop-
tera, though not strictly aquatic, are known to parasitize the eggs and
larvae of aquatic insects.
The change from the terrestrial to the aquatic habit has been a
gradual change of adaptation, not an abrupt one. Thus at present there
are some tipulid larv^ that inhabit comparatively dry soil; others live
in earth that is moist; many require a saturated soil near a body of
water and many, at length, are strictly aquatic Among beetles, also,
similar transitional stages are to be found.
Food. — Insects have become adapted to utilize with remarkable
success the immense and varied supply of food that the water affords.
Hosts of them attack such parts of plants as project above the surface of
the water, and the caterpillar of Paraponyx (Fig. 174) feeds on sub-
merged leaves, especially of Vallisneria, being in this respect almost
unique among Lepidoptera. Hydrophilid beetles and many other
aquatic insects devour submerged vegetation. The larvae of the chry-
someHd genus Donacia find both nourishment and air in the roots of
aquatic plants. Various Collembola subsist on floating alg^e, and larvae
of mosquitoes and black-flies on microscopic organisms near the surface,
while larvae of midges, Chironomus, find food in the sediment that accu-
mulates at the bottom of a body of water.
Predaceous species abound in the water. The backswimmer,
Notonecta (Fig. 227) approaches its prey from beneath, clasps it with
the front pair of legs and pierces it. The water scorpions, Nepa and
16s
i66
ENTOMOLOGY
Ranatra, likewise have prehensile front legs along with powerful piercing
organs. The electric light bugs, Belostoma and Benacus (Fig. 23) even
kill small fishes by their poisonous punctures. Some other kinds, as the
water-skaters (Gerridae, Fig. 228), depend on dead or disabled insects.
The species of Eydrophilus (Fig. 229) are to some extent carnivorous as
Fig. 227.- — Backswimmer, Notonecta
lata, natural size.
Pig. 228.
-Water-skater, Gerris remigis,
natural size.
larvae but phytophagous as imagines, while Dytiscidae (diving beetles)
are carnivorous throughout life. Aquatic insects eat not only other
insects, but also worms, crustaceans, mollusks or any other available
animal matter.
Even aquatic insects are not exempt from the attacks of parasitic
species. A few Hymenoptera actually enter the water to find their
victims, for example, the ichneumon Agriotypus,
which lays its eggs on the larvae of caddis flies.
Locomotion. — Excellent adaptations for
aquatic locomotion are found in the common
Hydrophilus triangularis (Fig. 229). Its general
form reminds one of a boat, and its long legs
resemble oars. The smoothly elHptical contour
and the polished surface serve to lessen resistance.
Owing to the form of the body (Fig. 230, A) and
the presence of a dorsal air-chamber under the
elytra, the back of the insect tends to remain
uppermost, while in the backswimmer, Notonecta
(Fig. 230, B), on the other hand, the conditions
are reversed, and the insect swims with its back
downward. The legs of Hydrophilus, excepting the
first pair, are broad and thin (Fig. 231, A) and the tarsi are fringed with
long hairs. When swimming, the "stroke" is made by the flat surface,
aided by the spreading hairs; but on the "recover," the leg is turned so
Fig. 229. — Hydroph-
ilus triangularis, nat-
ural size.
ADAPTATIONS OF AQUATIC INSECTS
167
as to cut the water, while the hairs fall back against the tarsus from the
resistance of the water, as the leg is being drawn forward. The hind
A B
Fig. 230. — Transverse sections of {A) Hydrophilus and (B) Nolonecla. e, elytron; h,
hemelytron; I, metathoracic leg.
legs, being nearest the center of gravity, are of most use in swimming,
though the second pair also are used for this purpose; indeed, a terrestrial
insect, finding itself in the
water, instinctively relies
upon the third pair of legs
for 1 ocomotion. Hydro-
philus uses its oar-like legs
alternately, in much the
same sequence as land
insects, but Cyhister and
other Dytiscidas, which
are even better adapted
than Hydrophilus for
aquatic locomotion, move
the hind legs simultane-
ously, and therefore can
swim in a straight line,
without the wobbling and
less economical m o v e-
ments that characterize
Hydrophilus.
Larvae of mosquitoes
propel themselves b y
means of lashing, or undu-
latory, movements of the
abdomen. A peculiar mode of locomotion is found in dragon fly
nymphs, which project themselves by forcibly ejecting a stream of
water from the anus.
Fig. 231. — Left hind legs of aquatic beetles. A,
Hydrophilus triangularis; B, Cybister fimbriolatus; c,
coxa; /, femur; s, spur; /, tarsus; ti, tibia; tr, tro-
chanter.
i08
ENTOMOLOGY
On account of the large amount of air that they carry about, most
aquatic imagines are lighter than the water in which they live, and
therefore can rise without effort, but can descend only by exertion, and
can remain below only by clinging to
chance stationary objects. The mosquito
larva (Fig. 232, ^) is often heavier than
water, but the pupa (Fig. 232, B) is lighter,
and remains clinging to the surface film.
The tension of this surface film is suffi-
cient to support the weight of an insect
up to a certain limit, provided the insect
has some means of keeping its body dry.
This is accompKshed usually by hairs,
set together so thickly that water cannot
penetrate between them. As the legs and
body of Gerris are rendered water-proof
by a velvety clothing of hairs, the insect,
though heavier than water, is able to skate
about on the surface. Gyrinus, by means
of a similar adaptation, can circle about
on the surface film, and minute collembo-
lans leap about on the surface as readily
as on land.
The modifications of the legs for swim-
ming have often impaired their usefulness
for walking, so that many aquatic Coleop-
tera and Hemiptera can move but awk-
wardly on land. When walking, it is inter-
esting to note, Cyhister and some other
aquatic forms no longer move their hind
legs simultaneously as they do in swim-
ming, but use them alternately, like ter-
restrial species.
The adaptations for swimming do not
necessarily affect the power of flight.
Dytiscus, Hydrophilus, Gyrinus, Notonecta, Benacus and many other
Coleoptera and Hemiptera leave the water at night and fly around,
often being found about electric lights.
Respiration. — Aquatic insects have not only retained the primitive,
or open {holopneustic) type of respiration, characterized by the presence
Fig. 232. — Larva {A) and pupa
{B) of mosquito, Culex pipiens.
r, respiratory tube; /, tracheal
gills.
ADAPTATIONS OF AQUATIC INSECTS 1 69
of spiracles, but have also developed an adaptive, or closed (apneustic)
type, for utilizing air that is mixed with water.
Through minor modifications of structure and habit, many holo-
pneustic insects have become fitted for an aquatic life. In these in-
stances the insects have some means of carrying down a supply of air
from the surface of the water. Thus the backswimmer, Notonecta,
bears on its body a silvery film of air entangled in closely set hairs,
which exclude the water. The whirhgig beetle, Gyrinus, descends
with a bubble of air at the end of the abdomen. Dytiscus and Hydro-
philus have each a capacious air-space between the elytra and the
abdomen, into which space the spiracles open. The water scorpions,
Nepa and Ranatra, have each a long respiratory organ composed of two
valves, which lock together to form a tube that communicates with the
single pair of spiracles situated near the end of the abdomen. The
mosquito larva, hanging from the surface film, breathes through a
cyhndrical tube (Fig. 232, A, r) projecting from the penultimate
abdominal segment; the pupa, however, bears a pair of respiratory
tubes on the back of the thorax (Fig. 232, B, r, r), which is now upward,
probably in order to facilitate the escape of the fly. The rat-tailed
maggot (Eristalis), three quarters of an inch long, has an extensile
caudal tube seven times that length, containing two tracheae terminating
in spiracles, through which air is brought down from above the mud in
which the larva lives. Similarly, in the dipterous larva, Bitlacomor pha
clavipes (Fig. 175), the posterior segments of the abdomen are attenu-
ated to form a long respiratory tube. The larva of Donacia appears
to have no special adaptations for aquatic respiration except a pair of
spines near the end of the body, for piercing air chambers in the roots
of the aquatic plants in which it dwells.
The simplest kind of apneustic respiration occurs in aquatic nymphs
such as those of Ephemerida and Agrionidae, whose skin at first is thin
enough to allow a direct aeration of the blood. This cutaneous res-
piration is possible during the early life of many aquatic species.
Branchial respiration is, however, the prevalent type among aquatic
nymphs and is perhaps the most important of their adaptive character-
istics. Thin-walled and extensive outgrowths of the integument, con-
taining tracheal branches or, rarely, only blood {Blood gills) enable
these forms to obtain air from the water. May fly nymphs (Figs. 20,
A ; 170), with their ample waving gills, offer familiar examples of branch-
ial respiration. Tracheal gills are very diverse in form and situation,
occurring in a few species of May fly nymphs on the thorax or head,
170
ENTOMOLOGY
though commonly restricted to the sides of the abdomen, where they
occur in pairs or in paired clusters (Fig. 20, A). Caudal gills are found
in agrionid nymphs (Fig. 173). The aquatic caterpillars of Pam^ow;>a
(Fig. 174) are unique among Lepidoptera in having gills, which are
filamentous in this instance.
Caddis worms, enclosed in their cases, maintain a current of water by
means of undulatory movements of the body, and the larvae and pupae
of most black-flies (Simuliidae, Fig. 233) secure a continuous supply of
fresh air simply by fastening themselves to rocks in swiftly flowing
streams.
Rectal respiration is highly developed in dragon fly nymphs. In
these, the rectum is lined with thousands of
tracheal branches, which are bathed by water
drawn in from behind, and then expelled.
All these kinds of respiration— cutaneous,
branchial and rectal — occur in young ephemerid
nymphs; while mosquito larvae have in addition
spiracular respiration.
With the arrival of imaginal life, tracheal
gills disappear, except in Perlidae, and even in
these insects the gills are of little, if any, use.
Marine Insects. — Except along the shore,
the sea is almost devoid of insect life, the excep-
tions being a few chironomid larvae which have
been dredged in deep water, and fifteen species
of Halohates (belonging to the same family as
our famihar pond-skaters), which are found on warm smooth seas,
where they subsist on floating animal remains.
Between tide-marks may be found various beetles and collembolans,
which feed upon organic debris; as the tide rises, the former retreat,
but the latter commonly burrow in the sand or under stones and become
submerged, for example the common Anurida maritima.
Insect Drift.— Seaweed or other refuse cast upon the shore harbors
a great variety of insects, especially dipterous larvae, staphylinid scaven-
gers and predaceous Carabidae. On the shores of inland ponds and
lakes a similar assemblage of insects may be found feeding for the most
part on the remains of plants or animals, or else on one another. During
a strong wind, the leeward shore of a lake is an excellent collecting
ground, as many insects are driven against it. On the shores of the
Great Lakes insects are occasionally cast up in immense numbers, form-
FlG. 233. — Simulium;.
A, larva; B, pupa, show-
ing respiratory filaments.
ADAPTATIONS OF AQUATIC INSECTS 17I
ing a broad windrow, fifty or perhaps a hundred miles long. Needham
has described such an occurrence on the west shore of Lake Michigan,
following a gale from the northeast. In this instance, a liter of the
drift contained nearly four thousand insects, of which 66 per cent, were
crickets (Nemobius), 20 per cent. Locustidae, and the remainder mostly
beetles (Carabidae, Scarabaeidae, Chrysomelidae, Coccinellidae, etc.),
dragon flies, moths, butterflies {Anosia, Pieris, etc.) and various
Hemiptera, Hymenoptera and Diptera. A large proportion of the insects
were aquatic forms, such as Hydrophilus, Cybister, Zaitha, and a species
of caddis fly; these had doubtless been carried out by freshets, while the
butterflies and dragon flies had been borne out by a strong wind from
the northwest, after which all were driven back to the coast by a north-
east wind. While some of these insects survived, notably Coccinellidae,
Trichoptera, Asilidae, Locustidae and Gryllidae, nearly all the rest were
dead or dying, including the dragon flies, flies, bumblebees and wasps.
Foraging Carabidae were observed in large numbers, also scavengers of
the families Staphylinidae, Silphidae and Dermestidae.
On the seashore and on the shores of the Great Lakes, the salient
features of insect life are essentially the same. Similar species occur in
the two places with similar biological relations, on account of the general
similarity of environment.
Origin of the Aquatic Habit. — The theory that terrestrial insects
have arisen from aquatic species is no longer tenable, for the evidence
shows that the terrestrial type is the more primitive. Aquatic insects
still retain the terrestrial type of organization, which remains unob-
scured by the temporary and comparatively slight adaptations for an
aquatic life. Thus, the development of tracheal gills has involved no
important modification of the fundamental plan of tracheal respiration.
It is significant, moreover, that the most generalized, or most primitive,
insects — Thysanura — are without exception terrestrial. Aquatic in-
sects do not constitute a phylogenetic unit, but represent various orders,
which are for the most part undoubtedly terrestrial, notwithstanding the
fact that a few of these orders (Plecoptera, Ephemerida, Odonata, Tri-
choptera) are now wholly aquatic in habit. Adaptations for an aquatic
existence have arisen independently and often, in the most diverse
orders of insects.
CHAPTER V
COLOR AND COLORATION
The naturalist distinguishes between the terms color and coloration.
A color is a single hue, while coloration refers to the arrangement of colors.
Sources of Color. — The colors of insects are classed as (i) pigmental
{chemical)., those due to internal pigments; (2) structural {physical),
those due to structures that cause interference or reflection of light;
and (3) combination colors {chemico-physical) , which are produced in
both ways at once.
Structural Colors. — The iridescence of a fly's wing and that of a
soap bubble are produced in essentially the same way. The wing, how-
ever, consists of two thin, transparent, slightly separated lamellae, which
diffract white light into prismatic rays, the color differences depending
upon differences in the distance between the two membranes.
The brilliant iridescent hues of many butterfly scales are due to the
diffraction of light by fine, closely parallel striae (Fig. 95) just as in the
case of the "dift'raction gratings" used by the physicist, which consist of
a glass or metalHc plate with parallel equidistant diamond rulings of
microscopic fineness. The particular color produced depends in both
cases upon the distance between the striae. Though almost all lepidop-
terous scales are striated, it is only now and then that the striae are
sufficiently close together to give diffraction colors. In a Brazilian
species of Apatura the iridescent scales have 1,050 striae to themilhmeter,
and in a species of Morpho, according to Kellogg, the iridescent pig-
mented scales have 1,400 striae per millimeter, the striae being only
.0007 mm. apart; while in some of the finest Rowland gratings they
number about 1,200 per millimeter.
In the well known diamond beetle the green dots of the elytra are
depressions from which spring brilliant and exquisitely colored scales,
the colors varying throughout the range of the spectrum; green, however,
predominating. These colors are due to diffraction from regular stria-
tions, with a "grating" space of a thousandth to a two-thousandth of a
millimeter. On immersing the specimen in oil or other liquid little or
no change is observed, except in those specimens in which a small
communicating aperture exists in the neck of the scale. The oil can be
172
COLOR AND COLORATION 1 73
seen gradually to till the interior, and simultaneously all trace of color
vanishes (except sometimes a faint greenish surface color). It appears,
then, that the color in this case is due to fine striations on the interior
surface of the scale. (Michelson.)
The interference coIofs of butterfly scales may be due, not only to
surface markings, but also to the lamination of the scale and to the
overlapping of two or more scales. In beetles the brilliant blues and
greens, and iridescence in general, are sometimes produced by minute
lines or pits that diffract the light. According to Tower, "The pits
alone, however, are powerless to produce any color; it is only when they
are combined with a highly reflecting and refractive surface lamella and
a pigmented layer below that the iridescent color appears. The action
of light is in this case the same as in the plain metaUic coloring, excepting
that each pit acts as a revolving prism to disperse different wave-lengths
of light in different directions, and the combined result is iridescence.
The existence of minute pits over the body surface is of common occur-
rence, but it is only when they are combined as above that iridescent
colors occur."
The production of color by "metallic" reflection deserves more
attention than it has received from naturalists. The metallic colors
of birds and insects have been studied precisely by Professor Michelson,
who has proved that they are due to the same causes in both animals
and metals. The metals, on account of their extraordinary opacity,
throw back practically all the light that strikes them, thus giving the
characteristic brilliant reflections; the distance to which light can pen-
etrate in most metals being only a small fraction of a light wave, so
that a wave-motion such as constitutes light, strictly speaking, can
not be propagated at all. As this opacity may be different for different
colors, some would be transmitted more freely than others, so that the
resulting transmitted light would be colored; and the reflected Ught
would be approximately complementary to the transmitted color.
(Michelson.) Thus the reflected light from the metal gold is yeUow,
the transmitted light being blue. In certain pigeons, peacocks, hum-
ming birds, as well as a number of butterflies, beetles and other insects,
the brilliant metaUic colors are due to an extremely thin surface film
which has optical qualities like those of metals. This film in the case
of the coppery wing cover of a beetle was calculated by Micheson to be
less than a ten-thousandth of a milHmeter in thickness.
In animals, as in metals, these colors are brilliant because a large
percentage of the incident light is reflected. The color of the reflected
174 ENTOMOLOGY
light is complementary to that of the transmitted. Furthermore, the
color of the reflected light changes when the surface is inclined, the color
always approaching the violet end of the spectrum as the incidence
increases. "If the color of the normal reflection is violet the Hght
vanishes (changing to ultra-violet), and if -the normal radiation be
infra-red it passes through red, orange, and yellow as the incidence
increases." (Michelson.)
Professor Michelson states that the metallic and spectrum colors
of the tiger beetles, CicindelidcB, are chiefly if not entirely true surface
or metalHc colors, produced by a film of ultra-microscopic thickness,
probably less than a ten-thousandth of a millimeter. This film must
be lacking in the dead black variety of Cicindela scutellaris, which is
without trace of color, hke a piece of black paper, Michelson is
inclined to attribute differences in the colors to differences in the chemi-
cal constitution of the film, and color changes during ontogeny to
changes in chemical constitution, but states that this would be very
difficult to demonstrate on account of the minuteness of the film.
(Shelford.)
Silvery white effects are usually caused by the total reflection of
light from scales or other sacs that are filled with air; the same silvery
appearance is given also by air-filled tracheae and by the air bubbles
that many aquatic insects carry about under water.
Violet, blue-green, coppery, silver and gold colors are, with few
exceptions, structural colors. (Mayer.)
Pigmental Colors. — These are either cuticular or hypodermal. The
predominant brown and black colors of insects are made by pigment
diffused in the outer layer of the cuticula (Fig. 90). Cockroaches are
almost white just after a molt, but soon become brown, and many
beetles change gradually from brown to black. In these cases it is
apparently significant that the cuticular pigments lie close to the surface
of the skin, i. e., where they are most exposed to atmospheric influences.
Gortner found that the black cuticular pigment in the Colorado potato
beetle {Leptinotarsa) and the brown or black . pigments of the tiger
beetles (Cicindela) belong to the group of melanins and are produced by
oxidation, induced by an oxidase; that when all oxygen is absent no
pigmentation takes place.
The cuticular pigments are derived, of course, from the underlying
hypodermis cells, and these cells themselves, moreover, usually contain
(i) colored granules or fatty drops which give red, yellow, orange and
sometimes white or gold colors as seen through the skin; (2) diffused
COLOR AND COLORATION 1 75
chlorophyll (green) or xanthophyll (yellow), taken from the food plant.
Unlike the structural colors, which are persistent, these hypodermal
colors often change after death, though less rapidly when the pigments
are tightly enclosed, as in scales or hairs. Though white and green are
structural colors as a rule, they are due to pigments in Pieridag, Lycaeni-
dae and some Geometridae.
Frequently a color pattern consists partly of cuticular and partly of
hypodermal colors, the hypodermal or sub-hypodermal color forming "a
groundwork upon which the pattern is cut out by the cuticular color."
(Tower.) Thus in the Colorado potato beetle, Leptinotarsa decemlineata,
the pattern ''is composed of a dark cuticular pigment upon a yellow
hypodermal background."
The pigment present in the cuticula of tiger beetles is essentially all
in the primary cuticula, and is always either brown or black. In
certain areas the primary cuticula is pigmented and in certain areas
clear and transparent. This gives the color pattern. The secondary
cuticula beneath the unpigmented areas is full of pore canals and large
air-filled interlamellar spaces, and these give the efifect of a white or
straw color depending upon the color of the secondary cuticula itself.
(Shelford.)
Combination Colors. — The splendid changeable hues of Apatura,
Euplcea and other tropical butterflies depend upon the fact that their
scales are both pigmented and striated. Under the microscope, certain
Apatura scales are brown by transmitted light and violet by reflected
light, and to the unaided eye the color of the wing is either brown or
violet, according as the light is received respectively from the pigment
or from the striated surfaces of the scales.
Nature of Pigments. — Some pigments are taken bodily from the
food; others are manufactured indirectly from the food, and some of
these are excretory products.
The green color of many caterpillars and grasshoppers is due to
chlorophyll, which tinges the blood and shows through the transparent
integument. Mayer has found that scales of Lepidoptera contain only
blood while the pigment is forming; that the first color to appear upon
the pupal wings is a dull ochre or drab — the same color that the blood
assumes when it is removed from the pupa and exposed to the air ; also
that pigments like those of the wings may be manufactured artificially
from pupal blood. Pieridae are peculiar in thenature of their pigments,
as Hopkins has shown. The white pigment of this family is uric acid
and the reds and yellows of Pieris, Colias and Papilio are due to deriva- .
176 ENTOMOLOGY
tives of uric acid; the yellow pigment, termed lepidotic acid, precedes
the red in time of appearance, the latter being probably a derivative
of the former. The green pigments of some Papilionidae, Noctuidse,
Geometridae and Sphingidae are also said by some investigators to be
products of uric acid, which in insects as in other animals is primarily
an excretory, or waste, product.
Effects of Food on Color. — Besides chlorophyll, to which various
caterpillars, aphids and other forms owe their green color, the yellow
constituent of chlorophyll, namely xanthophyll, frequently imparts its
color to plant-eating insects, while some phytophagous species are dull
yellow or brown from the presence of tannin, taken from the food plant.
Most pigments, however, are elaborated from the food by chemical
processes that are not well understood.
Many who have reared Lepidoptera extensively know that the color
of the imago is influenced by the character of the larval food, other con-
ditions being equal, and are able at will to effect certain color changes
simply by feeding the larvae from birth upon particular kinds of plants.
In this country we have few observations upon the subject, but in Europe
the effects of food upon coloration have been ascertained in the case of
many species of Lepidoptera. According to Gregson, Hybernia defolia-
ria is richly colored when fed upon birch, but is dull colored and almost
unmarked when fed on elm. Pictet, by feeding larvae of Vanessa
urticxB on the flowers instead of the leaves of the nettle obtained the
variety known as urticoides. Food affects the color of the larva also,
as Poulton found in the case of caterpillars of Tryphcena pronuba, all
from the same batch of eggs. When fed with only the white midribs
of cabbage leaves, the larvae remained almost white for a time, but
afterward showed a moderate amount of black pigment; when fed with
the yellow etiolated heart-leaves or the dark green external leaves,
however, the larvae all became bright green or brown — the same pigment
being derived indifferently from etiolin (probably the same substance
as xanthophyll) or chlorophyll.
Though the pigments may differ in color or amount according to
the kind of food, the color patterns vary without regard to food. Thus
Callosamia promethea, Leptinotarsa decemlineata (Colorado potato
beetle), CoccineUidae (lady-bird beetles) and a host of other insects
exhibit extensive individual variations in coloration under precisely
the same food conditions. Caterpillars of the same kind and age are
often very differently marked when feeding upon the same plant; for
example, Chloridea obsoleta (corn worm) and the sphingid Deilephila
COLOR AND COLORATION 1 77
Uneata. Furthermore, striking changes of coloration accompany each
molt in most caterpillars, but particularly those of butterflies, and
these changes may prove to have an important phylogenetic signifi-
cance. Individual differences of coloration apart from those due to the
direct action of food, light, temperature and other environmental
conditions are to be explained by heredity.
Effects of Light and Darkness.— Sunlight is an important factor in
the development of most animal pigments, as they will not develop in
its absence. The collembolan Anurida maritima is white at hatching,
but soon becomes indigo blue, unless shielded from sunhght, in which
event it remains white until exposed to the sunhght, when it assumes the
blue color. Subterranean or wood-boring larvae are commonly white
or yellow, but never highly colored. The most notable instances,
however, are furnished by cave insects. These, like other cavernico-
lous animals, are characteristically white or pale from the absence of
pigment, if they live in regions of continual darkness, but have more or
less pigmentation in proportion respectively to the greater or less
amount of sunlight to which they have access.
Curiously enough, light often hastens the destruction of pigment in
insects that are no longer alive, for which reason it is necessary to keep
cabinet specimens in the dark as much as possible. Life is evidently es-
sential for the sustention or renewal of the pigments.
A chrysalis not infrequently matches its surroundings in color. This
phenomenon has been investigated by Poulton, who has proved that the
color of the chrysalis is determined largely by the prevalent color of
the surroundings during the last few days of larval life. Larvae of the
cabbage butterfly, Pieris rapcB, raised upon the same food plant (all
other conditions being made as nearly equal as possible) produced dark
pupae if kept in darkness for a few days just before pupation; yellow
light arrested the formation of the dark pigment and gave green pupae;
while light colors in general gave light-colored pupae. This color
resemblance is commonly assumed to be of protective value, and per-
haps it is. Nevertheless, it is a direct effect of light, and does not need
to be explained by natural selection, even though it cannot be denied
that natural selection may have helped in its production.
Poulton extended his studies to the adaptive coloration of caterpillars
and has published the results of an extensive series of experiments which
prove that the colors of certain caterpillars also are directly produced by
the same colors in the surrounding light. Gastropacha quercifolia, which
always rests by day on the older wood of its food plant, was given black
1 78 ENTOMOLOGY
twigs, reddish brown sticks, lichens, etc., to rest upon, and though all the
larvae were from the same cluster of eggs, and had been fed in the same
way, each larva gradually assumed the color or colors of its resting place,
resulting in exquisite examples of protective resemblance, the most re-
markable of which were those in which the larvae assumed the variegated
coloration of lichens. Only the younger larvae, however, proved to be
susceptible to the colors of the environment; unlike those of Amphidasis
hetidaria, in which the older larvae also were sensitive to the surrounding
light. Here again, natural selection is unnecessary, even if not super-
fluous, as an explanation of this kind of protective coloration.
Professor W. M. Wheeler has suggested that "such phenomena as
the permanent protective coloration of insects may be regarded as the
stereotyped, highly specialized end-stage of a more ancient ability
actively to change color in response to color changes in the environment,
an abiHty still possessed by some primitive insects like the grasshoppers
and mantids, though much more pronounced in cephalopod mollusks,
fishes, amphibia and Hzards."
Effects of Temperature. — The amount of a pigment in the wing of a
butterfly depends in great measure upon the surrounding temperature
during the pupal stage, when the pigments are forming. Black or brown
spots have been enlarged artificially by subjecting chrysalides to cold;
hence it is probable that the characteristically large black spots on the
under side of the wings of the spring brood of our Cyaniris pseudargiolus
are simply a direct effect of cold upon the wintering chrysalides.
Similarly the spring brood (variety marcia) of Phyciodes tharos owes its
distinctive coloration to cold, as Edwards has proved experimentally.
Lepidoptera have been the subject of very many temperature experi-
ments, some of which will be mentioned presently in the consideration
of seasonal coloration.
Speaking generally, warmth (except in melanism) tends to induce a
brightening and cold a darkening of coloration, the darkening
being due to an increased amount of black or brown pigment. Temper-
ature, whether high or low, seldom if ever produces new pigments,
but simply alters the amount and distribution of pigments that are
present already.
Effects of Moisture. — Very Httle is known as to the effects of mois-
ture upon coloration. The dark colors of insular or coastal insects as
contrasted with inland forms, and the predominance of dull or suffused
species in mountainous regions of high humidity, have led observers
occasionally to ascribe melanism and sufusion to humidity. In these
COLOR AND COLORATION 1 79
cases, however, the possible influence of low temperature and other
factors must be taken into consideration. The experiments of Merrifield
and of Standfuss showed no effect of moisture upon lepidopterous pupae.
Pictet has found, however, that humidity acting on the caterpillars
of Vatiessa urtica and V. polychloros has a conspicuous effect on the
coloration of the butterflies. Thus when the caterpillars were fed for
ten days with moist leaves, the resulting butterflies had abnormal
black markings on the wings, and the same results followed when the
larvas were kept in an atmosphere saturated with moisture.
Climatal Coloration. — The brilliant and varied colors of tropical
insects are popularly ascribed to intense heat, light and moisture; and
the dull monotonous colors of arctic insects, similarly to the surrounding
climatal conditions Climate undoubtedly exerts a strong influence
upon coloration, but the precise nature of this influence is obscure and will
remain so until more is known about the effects separately produced by
each of the several factors that go to make up what is called cHmate.
The prevalence of intense and varied colors among tropical insects
is doubtless somewhat exaggerated, for the reason that the highly
colored species naturally attract the eye to the exclusion of the less
conspicuous forms. Indeed, Wallace assures us that, although tropi-
cal insects present some of the most gorgeous colors in the whole realm
of nature, there are thousands of tropical species that are as dull colored
as any of the temperate regions. Carabidae, in fact, attain their greatest
brilliancy in the temperate zone, according to Wallace, though butter-
flies certainly show a larger proportion of vivid and varied colors in the
tropics. Mayer finds, in the widely distributed genus Papilio, that 200
South American species display but 36 colors, while 22 North American
species show 17. While the number of species in South America is
nine times as great as in North America, the number of colors displayed
is only a little more than twice as great; hence Mayer concludes that
the richer display of colors in the tropics may be due to the far greater
number of species, which gives a better opportunity for color sports to
arise; and not to any direct influence of the climate. Furthermore, the
number of broods which occur in a year is much greater in the tropics
than in the temperate zones, so that the tropical species must possess a
correspondingly greater opportunity to vary.
Albinism and Melanism. — These interesting phenomena, wide-
spread among the higher animals, have often been attributed to tempera-
ture, but albinism and melanism are, in some instances at least,
strongly inherited without regard to temperature.
l8o ENTOMOLOGY
Albinism is exceptional whiteness or paleness of coloration, and is
due usually to deficiency of pigment, but in some instances (Pieridae)
to the presence of a white pigment.
The common yellow butterfly, Colias philodice, and its relatives,
are frequently albinic. Scudder observed that albinism among butter-
flies in America appears to be confined to a few Pieridae, and to be re-
stricted to the female sex; is more common in subarctic and subalpine
regions than in lower latitudes and altitudes, and only in the former
places includes all the females. At low altitudes, however, instead of ap-
pearing early in the year as might be expected, the albinic forms appear
during the warmer months.
The experiments made by Gerould on C. philodice show that the
number of albinic female offspring from white females crossed with
yellow males is in accordance with Mendelian law. Albinism is not
entirely confined to the female as Scudder thought, for white males
occur, though they are extremely rare. ''They may be expected in
regions where the white female is especially abundant" (Gerould).
In Europe there are many albinic species of butterflies, and they
are by no means confined to family Pieridae.
Melanism is unusual blackness or darkness of coloration. As to
how it is produced little is known, though warmth is probably the most
potent influence, and some attribute it to moisture, as was mentioned.
Pictet obtained partial melanism in Vanessa urticce and V. polychloros
by subjecting the larvae to moisture.
In warm latitudes, some females of our Papilio glaucus are blackish
brown with black markings, instead of being, as usual, yellow with
black markings. In the South, some males of the spring brood of
Cyaniris pseudargiolus are partly or wholly brown instead of blue.
A melanic male of Colias philodice occurs as an extremely rare muta-
tion. A melanic variety of pomace fly, Drosophila, with a black body,
follows the Mendelian law in its appearance in breeding experiments.
Seasonal Coloration. — When butterflies have more than one brood
in a year, the broods usually differ in aspect, sometimes so much that
their specific identity is revealed only by rearing one brood from
another. The same species may exist under two or more distinct
forms during the same season — in other words, may be seasonally dimor-
phic, trimorphic or polymorphic.
Thus Polygonia interrogationis has two forms, fabricii and umhrosa.
which differ not only in coloration, but even in the form of the wings
COLOR AND COLORATION
;8]
and the genitalia. In New England fahricii hibernates and produces
umbrosa. as a rule, while umhrosa usually yields fahricii.
The little, blue butterfly, Cyaniris pseudargiolus (Fig. 234), is poly-
morphic to a remarkable degree. In the high latitudes of Canada a
Fig. 234. — Cyaniris pseudargiolus;
A, form lucia; B, violacea; C, pseudargiolus proper.
Natural size.
single brood {lucia) occurs. About Boston the same spring brood ap-
pears, but under two forms: an earlier variety {lucia), which is small,
with large black markings beneath; and a later variety (violacea),
which is typically larger, with smaller black spots, though it varies
into the form lucia. Finally,
in summer, a third form
{pseudargiolus proper)
appears, as the product of
lucia or else the joint prod-
uct of lucia and violacea, and
this is still larger, but the
black spots are now faint.
In the warm South the spring
form is violacea, but while
some of the males are blue,
others are melanic, as just
mentioned — a dimorphic con-
dition which does not occur
in the North. Violacea then
produces pseudargiolus, in
which, however, all the males are blue.
' Iphiclides ajax (Fig. 235) is another polymorphic butterfly whose
life history is complex. The three principal varieties of this species,
known respectively as marcellus, telamonides and ajax, differ not only in
coloration, but also in size and form; marcellus appears first, in spring;
telamonides appears a little later (though before marcellus has disap-
peared); and ajax is the summer form; as the season advances the
Pig. 235. — Iphiclides ajax, form telamonides, on
flower of button bush. Reduced.
l82
ENTOMOLOGY
varieties become successively larger, with longer tails to the hind
wings.
Now Edwards submitted chrysalides of the summer form ajax to
cold and thereby obtained, in the same summer, butterflies with the
form of ajax but the markings of the spring form telamonides . Some of
the chrysalides, however, lasted over until the next spring and then gave
telamonides.
In Phyciodes tharos (Fig. 236) the spring and summer broods, termed
respectively marcia and morpheus, were at first regarded as distinct
species. In marcia the hind wings are heavily and diffusely marked
beneath with strongly contrasting colors, while in morpheus they are
plain and but faintly marked. Edwards placed upon ice eighteen
chrysalides that normally would have produced morpheus; but instead
Fig. 236. — Phyciodes tharos; A, spring form, marcia; B, summer form, morpheus; under
surfaces. Natural size.
of this, the fifteen imagines that emerged were all of the spring form
marcia and were smaller than usual. Pupae derived from eggs of marcia
gave, after artificial cooling, not morpheus , but marcia again. The
evident conclusion is that the distinctive coloration of the spring variety
is brought about by low temperature. In Labrador, only one brood
occurs — marcia; in New York, the species if digoneutic (two-brooded)
and in West Virginia polygoneuiic (several-brooded) .
Extensive temperature experiments upon seasonal dimorphism in
Lepidoptera have been conducted in Europe by some of the most com-
petent biologists. Weismann found that pupse of the summer form of
Pieris napi, if placd on ice, disclosed the darker winter form, usually
in the same season, though sometimes not until the next spring. It was
found impossible, however, to change the winter variety into the sum-
mer one by the application of heat. Similar results have attended the
important and much-discussed experiments of Dorfmeister, Weismann
and others upon Vanessa levana-prorsa and other species, from which it
has been inferred by Weismann that the winter form is the primary.
COLOR AND COLORATION 1 83
older, and more stable of the two forms, and the summer form a second-
ary, newer, and less stable variety; since the latter form only, as a rule,
responds much to thermal influences. Weismann argued that, in addi-
tion to the direct effect of temperature, alternative inheritance also
plays an important part in the production of seasonal varieties. He
tried to show, moreover, that each seasonal variety is colored in adapta-
tion to its particular environment and that this adaptation may have
been brought about by natural selection — though he did not succeed
in this respect.
In several instances, local varieties have been artificially produced
as results of temperature control. Thus Standfuss produced in Ger-
many, by the application of cold, individuals of Vanessa urticcB which
were indistinguishable from the northern variety polaris; and from
pupae of Vanessa cardui, by warmth, a very pale form like that found in
the tropics; and, by cold, a dark variety similar to one found in Lapland.
Shelford, by subjecting a pupa of a tiger beetle, C. tranqueharica
{vulgaris) to cold moist conditions (mean temperature, 12° C; moist)
obtained, in Chicago, a color variety hke one that occurs naturally in
the eastern mountains.
In a second instance, both pattern and color were modified by hot
dry conditions (mean temperature, 37° C; dry), and a variety obtained
such as occurs in the western states.
In a third experiment, both pattern and color were modified by hot
wet conditions (37° C; moist), and a variety produced like one in the
moist southern states.
These investigators and others, notably Merrifield and Fischer, have
accumulated a considerable mass of experimental evidence, the inter-
pretation of which is in many respects difficult, involving as it does, not
merely the direct effect of temperature upon the organism, but also deep
questions of heredity, including reversion, individual variation, and the
inheritance of acquired characters.
The seasonal increase in size that is noticeable, as in C. pseudargiolus
and /. ajax, is doubtless an expression of increasing metabolism due to
increasing temperature. Warmth, as is well known, stimulates growth,
and cold has a dwarfing effect. While this is true as a rule, there are
some apparent exceptions, however. Thus Standfuss found that some
caterpillars were so much stimulated by unusual warmth that they
pupated before they were sufficiently fed, and gave, therefore, under-
sized imagines. A moderate degree of warmth, however, undoubtedly
hastens growth.
1 84
ENTOMOLOGY
Sexual Coloration. — The sexes are often distinguished by colora-
tional as well as structural differences. Colorational antigeny (this
word signifying secondary sexual differences of whatever sort) is most
prevalent among butterflies, in which it is the extreme phase of that
IHHI
It-e^
■^ A
^^^
^^^ r't ^aj
^™- i? ^^
^^»- j^^ ^vj:^
fS^^^^-^L^Mk
l^^ff^f^'^-r-^Jm
W"^- ~>l^l
^k^ '^ /p
hIr*sLj»^L^^H
lK^w/''^'A
i^\vv'^-^ ^H
^Mfjti./'/ /A
1^'^^ ^^^1
^^Hh^// ^^Kk
^'v-X^^j^l
Fig. 237. — Pieris prolodice; male (on the left) and female (on the right). Natural size.
differentiation of ornamentation for which Lepidoptera are unrivaled.
The male of Pieris protodice (Fig. 237) has a few brown spots on the
front wings; the female is checkered with brown on both wings. In
Colias philodice (Fig. 238) and C. eurytheme the marginal black band of
the front wings is sharp and uninterrupted
in the male, but diffuse and interrupted by
yellow spots in the female. In the genus
Papilio the sexes are often distinguished by
colorational differences and in Hesperiidas
the males often have an oblique black dash
across the middle of each front wing. Callo-
samia promethea (Fig. 239), the gipsy moth
and many other Lepidoptera exhibit colora-
tional antigeny. In not a few Sesiidae the
sexes differ greatly in coloration. Thus in
the male of the peach tree borer {Aegeria
exitiosa) all the wings are colorless and
transparent; while in the female the front
wings are violet and opaque and the fourth
abdominal segment is orange above. The
same sex may present two types of coloration, as in males of Cyaniris
pseudargiolus and females oi Papilio glaucus, already mentioned. Papilio
merope, of South Africa, is remarkable in having three females, which are
entirely different in coloration from one another and from the male.
Fig. 238. — Colias philodice;
right fore wing of male (above)
and of female (below). Nat-
ural size.
COLOR AND COLORATION
i8S
There is no longer any doubt, it may be added, as to the specific
identity of these forms.
Next to Lepidoptera, Odonata most frequently show colorational
antigeny. The male of Calopteryx maculata is velvety black; the female
smoky, with a white pterostigmatal spot. Among Coleoptera, the male
of Hoplia trifasciata is grayish and the female reddish brown; a few
more examples might be
given, though sexual dif-
ferences in coloration are
comparatively rare among
beetles. Of Hymenoptera,
some of the Tenthredinidae
exhibit colorational
antigeny.
Among tropical butter-
flies there are not a few
instances in which the
special coloration of the
female is adaptive — har-
monizing with the sur-
roundings or else imitating
with remarkable precision
the coloration of another
species which is known
to be immune from the
attacks of birds — as de-
scribed beyond. In this
way, as Wallace suggests,
the egg-laden females may
escape destruction, as they
sluggishly seek the proper
plants upon which to lay
their eggs. Here would
be a fair field for the operation of natural selection.
In most insects, however, sexual differences in coloration are ap-
parently of no protective value and are usually so trivial and variable
as probably to be of no use for recognition purposes. The usual state-
ment that these differences facilitate sexual recognition is a pure as-
sumption, in the case of insects, and one that is inadequate in spite of
its plausibility, for (i) it is extremely improbable from our present
Fig. 239.
Callosamia promethea. A, male, clinging to
cocoon; B, female. Reduced.
I 86 ENTOMOLOGY
knowledge of insect vision that insects are able to perceive colors except
in the broadest way, namely, as masses; (2) the great majority of insect
species show no sexual differences in coloration; (3) when colorational
antigeny is present it is probably unnecessary,- to say the least, for
sexual recognition. Thus, notwithstanding the marked dissimilarity
of coloration in the two sexes of C. promethea, the males, guided by an
odor, seek out their mates even when the wings of the female have been
amputated and male wings glued in their place, as Mayer found.
Hence, when useless, colorational antigeny cannot have been de-
veloped by natural selection and may be due simply to the extended
action of the same forces that have produced variety of coloration in
general.
Origin of Color Patterns. — Tower, who has written an important
work on the colors and color patterns of Coleoptera, finds that each of
the black spots on the pronotum of the Colorado potato beetle (Fig. 240)
"is developed in connection with a muscle, and marks the point of at-
tachment of its fibres to the cuticula." Thus the color pattern, in its
origin, is not necessarily useful. This point is so important that we
quote Tower's conclusions in full. ''The most important and widely
disseminated of insect colors are those of the cuticula . . . these
colors develop as the cuticula hardens, and appear first, as a rule, upon
sclerites to which muscles are attached. In one of the earlier sections of
this paper I showed that the pigment develops from before backward
and, approximately, by segments, excepting that it may appear upon
the head and most posterior segments simultaneously.
"In ontogeny color appears first, as a rule, over the muscles which
become active first, or upon certain sclerites of the body. These are
usually the head muscles, although exceptions are not infrequent. It
should be remembered that as the color appears the cuticula hardens,
and, considering that muscles must have fixed ends for their action, it
seems that there is a definite relation between the development of color,
the hardening of the cuticula, and the beginning of muscular activity;
the last being dependent upon the second, and, incidentally, accom-
panied by the first. As muscular activity spreads over the animal the
cuticula hardens and color appears, so that color is nearly, if not
wholly, segmentally developed.
"The relation which exists between cuticular color and the stift'ening
of the cuticula is thus a physiological one, the cuticula not being able to
harden without becoming yellow or brown. What bearing has this
upon the origin of color patterns? In the lower forms of tracheates,
COLOR AND COLORATION 1 87
such as the Myriapods, colors appear as segmental repetitions of spots
or pigmented areas which mark either important sclerites or muscle
attachments. On the abdomens of insects, where segmentation is best
observed, color appears as well-defined, segmentally arranged spots,
but on the thorax segmentation is obscured and lost upon the head. Of
what importance, then is pigmentation? And how did it arise? If the
ontogenetic stages offer any basis for phylogenetic generalization, we
may conclude that cuticula color originated in connection with the
hardening of the integument of the ancestral tracheates as necessary to
the muscular activity of terrestrial life. The primitive colors were
yellows, browns and blacks, corresponding well with the surroundings
in which the first terrestrial insects are supposed to have lived. The
color pattern was a segmental one, showing repetition of the same spots
upon successive segments, as upon the abdomen of Coleoptera.
"So firmly have these characters become ingrained in the tracheate
series, and so important is this relation of the hardening of the cuticula
to the musculature and to the formation of body sclerites, that even the
most specialized forms show this primitive system of coloration; and,
although there may be spots and markings which have no connection
with it, still the chief color areas are thus closely associated."
Development of Color Patterns. — Although the causes of colora-
tion are, for the most part, obscure, it is possible, nevertheless, to point
out certain paths along which coloration appears to have developed.
These paths have been determined by the comparison of color patterns
in kindred groups of insects and the study of colorational variations in
adults of the same species. Butterflies, moths and beetles have
naturally been preferred as subjects by most students.
The most primitive colors among moths are uniform dull yellows,
browns and drabs — the same colors that the pupal blood assumes when
it is dried in the air. These simple colors prevail on the hind wings of
most moths and on the less exposed parts of the wings of highly colored
butterflies. The hind wings of moths are, as a rule, more primitively
colored than the front ones because, as Scudder says, "all differentiation
in coloring has been greatly retarded by their almost universal conceal-
ment by day beneath the overlapping front wings." Exceptions to
this statement are found in Geo'metridas and such other moths as rest
with all the wings spread. "In such hind wings we find that the sim-
plest departure from uniformity consists in a deepening of the tint next
the outer margin of the wing; next we have an intensification of the
deeper tint along a line parallel to the margin; it is but a step from this
1 88 ENTOMOLOGY
condition to a distinct line or band of dark color parallel to the margin.
Or the marginal shade may, in a similar way, break up into two or more
transverse and parallel submarginal lines, a very common style of
ornamentation, especially in moths. Or, again, starting with the
submarginal shade, this may send shoots or tongues of dark color a
short distance toward the base, giving a serrate inner border to the
marginal shade; when now this breaks up into one, two, or more lines
or narrow stripes, these stripes become zigzag, or the inner ones may be
zigzag, while the outer ones are plain — a very common phenomenon.
"A basis such as this is .sufficient to account for all the modifications
of simple transverse markings which adorn the wings of Lepidoptera."
Briefly, one or more bands may break up into spots or bars, the
breaks occurring either between the veins or, more commonly, at the
veins; and in the latter event, short bars or more or less quadrate or
rounded spots arise in the interspaces. From simple round spots there
may develop, as Darwin and others have shown, many-colored eye-like
spots, or ocelli.
Mayer gives the following laws of color pattern: "(a) Any spot
found upon the wing of a butterfly or moth tends to be bilaterally sym-
metrical, both as regards form and color; and the axis of symmetry is a
line passing through the center of the interspace in which the spot is
found, parallel to the longitudinal nervures. (b) Spots tend to appear
not in one interspace only, but in homologous places in a row of adjacent
interspaces, (c) Bands of color are often made by the fusion of a row
of adjacent spots, and, conversely, chains of spots are often formed by
the breaking up of bands, (d) When in process of disappearance, bands
of color usually shrink away at one end. (e) The ends of a series of spots
are more variable than the middle. (/) The position of spots situated
near the outer edges of the wing is largely controlled by the wing folds
or creases."
These results have been arrived at chiefly by the study of the varia-
tions presented by color patterns.
Variation in Coloration. — It is safe to say that no two insects are
colored exactly alike Some species, however, are far more variable
than others. Catocala ilia, for example, occurs under more than fifty
varieties, each of which might be given a distinctive name, were it not
for the fact that these varieties run into one another. One may examine
hundreds of potato beetles {L. decemlineata) without finding any two
that have precisely the same pattern on the pronotum. The range of
COLOR AND COLORATION 1 89
this variation in this species is partially indicated in Fig. 240, and that
of Cicindela in Fig. 241.
Individuals of Cicindela vary in pattern in a few definite directions,
and the patterns that characterize the various species appear to be
tixations of individual variations. According to Dr. G. H. Horn: (i)
The type of marking is the same in all our species. (2) Assuming a well-
marked species, tranqueharica {vulgaris, Fig. 241, /) as a central type,
the markings of other species vary from that type, (a) by a progressive
spreading of the white, {b) by a gradual thinning or absorption of the
white, (c) by a fragmentation of the markings, {d) by linear supplemen-
tary extension. (3) Many species are practially invariable (i.e., the
individual variations are small in amount as compared with those in
other species) . These fall into two series : (a) those of the normal type,
as tranqueharica, hirticoUis and tenuisignata; (b) those in which some
modification of the type has become permanent, probably through
isolation, as marginipennis, togala and lemniscata. (4) Those species
which vary do so in one direction only. New types of pattern, of
specific value, appear to have arisen by the isolation and perpetuation
of individual variations.
. Professor Shelford, in his important monograph on the colors of
these beetles, draws the following conclusions, among others:
Longitudinal stripes in which pigment usually occurs lie in the area
of the chief tracheal trunks of the elytron; there are seven cross bands in
which pigment does not develop; the second and third and fifth and
sixth of these are often joined to make one of each pair.
Pigment usually occurs about the bases of hairs, which usually lie
in the lines of the tracheae.
In ontogeny the elytra show a spotted condition corresponding to the
system of cross bands and longitudinal stripes. The longitudinal
stripes are usually more pronounced.
The characteristic markings of the group are composed of spots or
elements joined in the longitudinal light stripe areas and areas of cross
bands, with the loss of various spots or elements which occur in onto-
geny; joinings are sometimes obHque, and when so markings are some-
times parallel with the curved end of the elytron.
Certain particular types of markings made up of a few elements joined
in a particular way characterize the majority of species of the group.
These markings as derived from the cross and longitudinal bands are
angular; reduction of angles, straightening and turning into oblique
I go ENTOMOLOGY
positions parallel with the end of the elytron characterize modifications
of markings. The response to stimuli (high temperature) is in the
same direction.
Response to other stimuli appears to be in the direction of
concentric extension of the markings.
The color patterns and structure to which they are related constitute
a mechanism, the directions of movement of which are hmited, i.e.,
easier in some directions than others; the color pattern plans break
when the related structures do; hereditary changes and fluctuations
due to stimulation during ontogeny are in the same direction; laws
governing the mechanism are the same throughout.
Variations in general fall into two classes: continuous {individual
variations) and discontinuous (mutations) . The former are always pres-
ent, are slight in extent and intergrade with one another; they are
distributed symmetrically about a mean condition. The latter are
occasional, of considerable extent and sharply separated from the
normal condition.
R. H. Johnson published an important statistical study on evo-
lution in the color pattern of the lady-beetles. He found both con-
tinuous and discontinuous variations present; that the color pattern is
capable of modification by the environment; that some modifications
are hereditary characters and others not.
Replacements. — Examples of the replacement of one color by
another are familiar to all collectors. The red of Vanessa atalanta and
CoccinelHdae may be replaced by yellow. These two colors in many
butterflies and beetles are due to pigments that are closely related to
each other chemically. Thus in the chrysomeHd Lina lapponica
the beetle at emergence is pale but soon becomes yellow with black
markings, and after several houts, under the influence of sunlight, the
yellow changes to red ; the change may be prevented, however, by keep-
ing the beetle in the dark. After death, the red fades back through
orange to yellow, especially as the result of exposure to sunlight.
Yellow in place of red, then, may be attributed to an arrested develop-
ment of pigment in the living insect and to a process of reduction in the
dead insect, metabolism having ceased.
Yellow and green are similarly related. The stripes of Pcecilocapsus
lineatus are yellow before they become green, and after death fade back
to yellow. As the green pigment in most, if not all, phytophagous in-
sects is chlorophyll, these color changes are probably similar to those
that occur in leaves. Leaves grown in darkness are yellow, from the
COLOR AND COLORATION
^ ■•»/•*-
U'
12
m
16
•\ s
Fig. 240. — Colorational variations of the pronotum of the Colorado potato beetle, Lepti
notarsa decemlineata.
ENTOMOLOGY
m
\ fi
Fig. 241. — Elytral color patterns of Cicindela. 1—8 illustrate reduction^of dark
area; 9-14, extension of dark area; 15, 16, formation of longitudinal vitta; 17, 18, linear ex-
tension of markings, i, C. tranquebarica; 2, fortnosa; 3, formosa; 4, pamphila; 5, limhala; 6,
togata; 7, gratiosa; 8, hamala; 9, tenuisignata; 10, marginipennis; 11, carthagena; 12, sex-
giUtata; 13, carthagena; 14, splendida; 15, pusilla; 16, lemniscata; 17, gabhi; 18, dorsalis. —
After Horn, from Entomological News.
COLOR AND COLORATION 1 93
presence of etiolin, and do not turn green until they are exposed to sun-
light (or electric light), without which chlorophyll does not develop;
and as metabolism ceases, chlorophyll disintegrates, as in autumn,
leaving its yellow constituent, xanthophyll, which is very likely the
same substance as etiolin.
Cicindela sexguttata and Calosoma scrutator are often blue in place of
green. These colors in these beetles are structural, and their variations
are to be attributed to slight differences in the structure of the surface.
Green grasshoppers occasionally become pink toward the close of
summer. No explanation has been offered for this phenomenon, though
it may be remarked that when grasshoppers are killed in hot water the
normal green pigment turns to pink.
These changes of color are apparently of no use to the insect, being
merely incidental effects of Hght, temperature or other inorganic
influences.
CHAPTER VI
ADAPTIVE COLORATION
Protective Resemblance. — Every naturalist knows of many ani-
mals that tend to escape detection by resembling their surroundings.
This phenomenon of protective resemblance is richly exemplified by in-
sects, among which one of the most remarkable cases is furnished by the
Kallima butterflies, especially K. inachis of India and K. paralekta of the
Malay Archipelago. The former species (Fig 242) is conspicuous when
on the wing; its bright colors, however, are confined to the upper surfaces
of the wings, and when these are folded together, as in repose, the insect
Fig. 242.-
-Kallima inachis; A, upper surface; B, with wings closed, showing resemblance
to a leaf. X 3-^.
resembles to perfection one of the dead leaves among which it is accus-
tomed to hide. The form, size and color of the leaf are accurately re-
produced, the petiole being simulated by the tails of the wings. Two
parallel shades, one light and one dark, represent, respectively, the
illuminated and the shaded side of a mid-rib, and the side-veins as well
are imitated; there are even small scattered black spots resembling
those made on the leaf by a species of fungus. Furthermore, the butter-
fly habitually rests, not among green leaves, where it would be conspicu-
ous, but among leaves with which it harmonizes in coloration.
Notwithstanding some discussion as to whether it usually rests in pre
^9\
ADAPTIVE COLORATION
195
cisely the same position as a leaf, this insect certainly deceives experi-
enced entomologists and presumably eludes birds and other enemies by
means of its deceptive coloration.
Some of the tropical Phasmida^ counterfeit sticks, green leaves, or
dead leaves with minute accuracy. Our common phasmids, Diaphero-
Fig. 243. — Manomera hlatchleyi, on a twig.
Natural size.
Fig. 244. — Calocala lacrymosa; A, upper sur-
face; B, with wings closed, and resting on bark.
Reduced.
mera femorata and Manomera hlatchleyi (Fig. 243), are well known as
"stick insects;" indeed, it is not necessary to go beyond the temperate
zone to find plenty of examples of protective resemblance. Geometrid
caterpillars imitate twigs, holding the body stiffly from a branch and
frequently reproducing the form and coloration of a twig with striking
exactitude; and the moths of the same family are often colored like the
bark against which they spread their wings. Even more perfectly do the
Catocala moths resemble the bark upon which they rest (Fig. 244), with
their conspicuous and usually showy hind wings concealed under the pro-
196
ENTOMOLOGY
tectively colored front wings. The caterpillars of Basilarchia archippus
and Papilio thoas, as well as other larvae and not a few moths, resemble
closely the excrements of birds. Numerous grass-eating caterpillars are
striped with green, as is also a sphingid species {Ellema harrisii) that
lives among pine needles." The large green sphinx caterpillars (Fig. 66)
perhaps owe their inconspicuousness partly to their oblique lateral
stripes, which cut a mass of green into smaller areas. The caterpillar
of Schizura ipomosce (Fig. 245), which is green with brown patches, rests
for hours along the eaten or torn edge of a basswood leaf, in which posi-
FiG. 245. — Caterpillar of Schizura ipomcea clinging to a torn leaf. Natural size.
tion it bears an extremely deceptive resemblance to the partially dead
border of a leaf. The weevils that drop to the ground and remain
immovable are often indistinguishable to the collector on account of
their Hkeness to bits of soil or little pebbles. Everyone has noticed
the extent to which some of the grasshoppers resemble the soil in color.
The CaroHna locust, Dissosteira Carolina, which varies greatly in
color, ranging from ashy gray to yellowish or to reddish brown, is
commonly found on soil of its own color. Along the Atlantic coast, the
seaside locust, Trimerotropis maritima, is practically invisible against
the gray sand of the seashore, to which it restricts itself. The same
species of grasshopper occurs inland also, as in Illinois and Michigan,
along the shores of lakes, and is then pale brown, Hke the sands that it
ADAPTIVE COLORATION
197
frequents. Another grasshopper of the same genus, Trimerotropis
saxatilis (Fig. 246) occurs only on rock-surfaces, either bare or Hchen-
crusted. This grasshopper, mottled with several colors but especially
yellow, black and greenish, is conspicuous when flying but indistinguish-
able when resting on a patch of lichens (Fig. 246 B) . Where the grass-
hopper occurs among Hchen-covered rocks, as in southern IlHnois, it
does not ahght by haphazard as a rule, but habitually flies from one
patch of lichens to another.
Instances such as this give support to the opinion that "protective
resemblances" are not always merely accidental occurrences; since the
protective colors are rendered effective by special habits of the insect.
Pig. 246. — Triynerolropis saxatilis. A, with wings of right side spread. B, with wings
closed, and resting on lichens. Natural size.
This particular grasshopper, it may be added, is sluggish, and incKned
to remain where it alights — an advantageous habit under the circum-
stances. The case is not so simple as that of a caterpillar that is green
simply because it feeds on chlorophylls.
Adventitious Resemblance. — If, instead of hastily ascribing all
cases apparently of protective resemblance to the action of natural
selection, one inquires into the structural basis of the resemblance in
each instance, it is found that some cases can be explained, without the
aid of natural selection, as being direct effects of food, light or other
primary factors. Such cases, then, are in a sense accidental. For ex-
ample, many inconspicuous green insects are green merely because
chlorophyll from the food-plant tinges the blood and shows through the
skin. If it be argued that natural selection has brought about a thin
and transparent skin, it may be replied that the skin of a green cater-
198 ENTOMOLOGY "
pillar is by no means exceptional in thinness or transparency. More-
over, many leaf-mining caterpillars are green, simply because their food
is green; for, living as they do within the tissues of leaves and surrounded
by chlorophyll, their own green color is of no advantage, but is merely
incidental.
Again, in the "protectively" colored chrysaHdes experimented upon
by Poulton, the color was directly influenced by the prevailing color
of the light that surrounded the larva during the last few days before
pupation. Of course, it is conceivable that natural selection may have
preserved such individuals as were most responsive to the stimulus of
the surrounding light; nevertheless the fact remains that these resem-
blances do not demand such an explanation, which is, in other words,
superfluous.
Indeed, a great many of the assumed examples of "protective re-
semblance" are very far-fetched. On the other hand, when the re-
semblance is as specific and minutely detailed as it is in the Kallima
butterflies — where, moreover, special instincts are involved — the phe-
nomenon can scarcely be due to chance; the direct and uncombined
action of such factors as food or light is no longer sufiicient to explain
the facts — although these and other factors are undoubtedly important
in a primary, or fundamental, way. Here natural selection becomes
useful, as enabling us to understand how original variations of structure
and instinct in favorable directions may have been preserved and ac-
cumulated until an extraordinary degree of adaptation has been attained.
Value of Protective Resemblance.— The popular opinion as to
the efficiency of protective resemblances is undoubtedly an exaggerated
one, owing mainly to the false assumption that the senses of the lower
animals are co-extensive in range with our own. As a matter of fact,
birds detect insects with a facility far superior to that of man, and
destroy them by the wholesale, in spite of protective coloration. Thus,
as Judd has ascertained, no fewer than three hundred species of birds
feed upon protectively colored grasshoppers, which they destroy in
immense numbers, and more than twenty species prey upon the twig-
like geometrid larvae; while the weevils that look like particles of soil,
and the green-striped caterpillars that assimilate with the surrounding
foliage are constantly to be found in the stomachs of birds.
After all, however, protective resemblance may be regarded as ad-
vantageous upon the whole, even if it is ineffectual in thousands of in-
stances. An adaptation may be successful even if it does fall short of
perfection; and it should be borne in mind that the evolution of protect-
ADAPrrV'E COLORATION 1 99
ive resemblances among insects has probably been accompanied on the
part of birds by an increasing ability to discriminate these insects from
their surroundings.
Warning Coloration. — In strong contrast to the protectively
colored species, there are many insects which are so vividly colored as
to be extremely conspicuous amid their natural surroundings. Such
are many Hemiptera (LygcBus, Murgantia), Coleoptera {Necrophorus,
Lampyridae, Coccinellidae, Chrysomelida;), Hymenoptera (MutilHdae,
Vespidie), and numerous caterpillars and butterflies. Conspicuous col-
ors, being frequently — though not always — associated with qualities
that render their possessors unpalatable or offensive to birds or other
enemies, are advantageous if, by insuring ready recognition, they ex-
empt their owners from attack.
Efficiency of Warning Colors. — Owing to much disagreement as
to the actual value of "warning" colors, several investigators have made
many observations and experiments upon the subject. Tests made by
offering various conspicuous insects to birds, lizards, frogs, monkeys and
other insectivorous animals have given diverse results, according to
circumstances. Thus, one gaudy caterpillar is refused by a certain bird
at once, or else after being tasted, but another and equally showy cater-
pillar is eaten without hesitation. Or, an insect at first rejected may at
length be accepted under stress of hunger; or a warningly colored form
disregarded by some animals is accepted by others. Moreover, some
of the experiments with captive insectivorous animals are open to ob-
jection on the score of artificiality.
Nevertheless, from the data now accumulated, there emerge some
conclusions of definite value. Frank Finn, whose conclusions are quoted
beyond, has found in India that the conspicuous colors of some butter-
flies, (Danainae, Acrcsa, violce, Delias eucharis, Papilio aristolochice) are
probably effective as "warning" colors. Marshall found in South
Africa that mantids, which would devour most kinds of butterflies, in-
cluding warningly colored species, refused Acrcea, which appeared to be
not only distasteful but even unwholesome; Acrcea is eaten, however,
by the predaceous Asilidse, which feed indiscriminately upon insects —
for example, beetles, dragon flies and even stinging Hymenoptera. The
masterly studies of Marshall and Poulton strongly support the general
theory of warning coloration.
In this country, much important evidence upon the subject has been
obtained by Dr. Judd from an extensive examination of the stomach-
contents of birds, supplemented by experiments and field observations.
200 ENTOMOLOGY
Judd says that the harlequin cabbage bug (Murgantia histrionica) and
other large showy bugs are usually avoided by birds; that the showy,
ill-flavored lady-beetles (Coccinellidas) and Chrysomelidae such as the
elm leaf beetle, Diabrotica, and Leptinotarsa (Doryphora), possess
comparative immunity from birds; and that Macrodactylus, Chauliog-
nathus and Cyllene are highly exempt from attack. Such cases, he
adds, are comparatively few among insects, however, and in general,
warning colors are effective against some enemies but ineffective against
others.
Generally speaking, hairs, stings and other protective devices are
accompanied by conspicuous colors — though there are many exceptions
to this rule. These warning colors nevertheless fail to accomplish their
supposed purpose in the following instances, given by Judd. Taking in-
sects that are thought to be protected by an offensive odor or a dis-
agreeable taste: Heteroptera in general are eaten by all insectivorous
birds, the squash bug by hawks and the pentatomids by many birds;
among Carabidse with their irritating fluids, Harpalus caliginosus and
pennsyhanicus are food for the crow, catbird, robin and six others;
Carabus and Calosoma are relished by crows and blackbirds; Silphidae
are taken by the crow, loggerhead shrike and kingbird ; and Leptinotarsa
decemlineata is eaten by at least six kinds of birds: wood thrush, rose-
breasted grosbeak, quail, crow, cuckoo and catbird. Of hairy and spiny
caterpillars, Arctiidae are eaten by the robin, bluebird, catbird, cuckoo
and others; the larvae of the gipsy moth are food for the blue-jay, robin,
chickadee, Baltimore oriole and many others [thirty-one birds, in Massa-
chusetts]; and the spiny caterpillars of Vanessa antiopa are taken by
cuckoos and orioles. Of stinging Hymenoptera, bumblebees are eaten
by the bluebird, blue- jay and two flycatchers; the honey bee, by the
wood pewee, phoebe, olive-sided flycatcher and kingbird; Andrena by
many birds, and Vespa and Polistes by the red-bellied woodpecker, king-
bird, and yellow-belhed flycatcher.
These facts by no means invalidate the general theory, but they do
show that "disagreeable" qualities and their associated color signals
are of httle or no avail against some enemies. The weight of evidence
favors the theory of warning coloration in a qualified form. While con-
spicuous colors do not always exempt their owners from destruction,
they frequently do so, by advertising disagreeable attributes of one sort
or another.
The evolution of warning coloration is explained by natural selec-
tion; in fact, we have no other theory to account for it. The colors
ADAPTIVE COLORATION . 20I
themselves must have been present, however, before natural selection
could begin to operate; their origin is a question quite distinct from that
of their subsequent preservation.
Protective Mimicry. — This interesting and highly involved phe-
nomenon is a special form of protective resemblance in which one species
Pig.
-A, Anosia plexippus, the "model;" B, Basilarchia archippus, the
Natural size.
imitates the appearance of another and better protected species, there-
by sharing its immunity from destruction. Though it attains its high-
est development in the tropics, mimicry is well illustrated in temperate
regions. A familiar example is furnished by Basilarchia archippus
(Fig. 247, B), which departs widely from the prevailing dark coloration
of its genus to imitate the milkweed butterfly, Anosia plexippus. The
latter species, or "model," appears to be unmolested by birds, and the
former species, or "mimic," is thought to secure the same exemption
202 ENTOMOLOGY
from attack by being mistaken for its unpalatable model. The common
drone-fly, Eristalis tenax (Fig. 248, B) mimics a honey bee in form, size,
coloration and the manner in which it buzzes about flowers, in company
with its model; it does not deceive the kingbird and the flicker, however.
Some Asilidae (robber flies) are remarkably hke bumblebees in superfi-
cial appearance and certain Syrphus flies (flower flies) mimic wasps
with more or less success. The beetle Casnonia bears a remarkable
resemblance to the ants with which it lives.
The classic cases are those of the Amazonian Heliconiidae and
Pieridae, in which mimicry was first detected by Bates. The Heli-
coniidae are abundant, vividly colored and eminently free from the
attacks of birds and other enemies of butterflies, on account of their
Fig. 248. — Protective mimicry. A, drone bee, Apis melUfera; B, drone fly, Eristalis tenax.
Natural size.
disagreeable odor and taste. Some of the Pieridae — a family funda-
mentally different from Hehconiidae — imitate the protected Heliconiidae
so successfully, in coloration, form and fhght, that while other Pieridae
are preyed upon by many foes, the mimicking species tend to escape
attack.
The family Heliconiidae, referred to by Bates, comprised what are
now known as the subfamilies Heliconiinae, Ithomiinae and Danainae;
simflarly, Pieridae and Papilionidas are now often termed respectively
Pierinae and Papilioninae. Ithomiinae are mimicked also by PapiHo-
ninae and by moths of the famihes Castniidae and Pericopidae.
The discoveries of Bates in tropical South America were paralleled
and supported by those of Wallace in India and the Malay Archipelago
(where Danainae are the chief "models"), and of Trimen in South Africa
(where Acraeinae and Danainae serve as models). Trimen discovered a
most remarkable case, in which three species of Danais are mimicked,
each by a distinct variety of the feijiale of Papilio cenea {merope).
ADAPTR'E COLORATION 203
So much for that kind of mimicry — but how is the following kind to
be explained? The Ithomiinoe of the Amazon valley have the same
form and coloration as the Heliconiinae, but the Ithomiime themselves
are already highly protected. The answer is that this resemblance is of
advantage to both groups, as it minimizes their destruction by birds —
these having to learn but one set of warning signals instead of two.
This is the essence of Miiller's famous explanation, which will presently
be stated with more precision. There are two kinds of mimicry, then:
(i) the kind described by Bates, in which an edible species obtains
security by counterfeiting the appearance of an inedible species; (2) that
observed by Bates and interpreted by Miiller, in which both species are
inedible. These two kinds are known respectively as Batesian and
Miillerian mimicry, though some writers prefer to limit the term mimi-
cry to the Batesian type.
Wallace's Rules. — The chief conditions under which mimicry occurs
have been stated by Wallace as follows:
"i. That the imitative species occur in the same area and occupy
the very same station as the imitated.
"2. That the imitators are always the more defenceless.
"3. That' the imitators are always less numerous in individuals.
"4. That the imitators differ from the bulk of their aUies.
"5. That the imitation, however minute, is external and visible
only, never extending to internal characters or to such as do not affect
the external appearance."
These rules relate chiefly to the Batesian form of mimicry and need
to be altered to apply to the Miillerian kind.
The first criterion given by Wallace is evidently an essential one and
it is sustained by the facts. It is also true that mimic and model occur
usually at the same time of year; Marshall found many new instances
of this in South Africa. In some cases of mimicry, strange to say, the
precise model is unknown. Thus some Nymphalidae diverge from their
relatives to mimic the Euploeinae, though no particular model has been
found. In such instances, as Scudder suggests, the prototype may exist
without having been found; may have become extinct; or the species
may have arrived at a general resemblance to another group without
having as yet acquired a likeness to any particular species of the group,
the general likeness meanwhile being profitable.
The second condition named by Wallace is correct for Batesian
but not for Miillerian mimicry.
The fulfilment of the third condition is requisite for the success
204 ENTOMOLOGY
of Batesian mimicry. Bates noted that none of the pierid mimics were
so abundant as their heliconiid models. If they were, their protection
would be less; and should the mimic exceed its model in numbers,
the former would be more subject to attack than the latter. Some-
times, indeed, as Miiller found, the mimic actually is more common than
the model; in which event, the consequent extra destruction of the
mimic would — at least theoretically — reduce its" numbers back to the
point of protection.
In Miillerian mimicry, however, the inevitable variation in abun-
dance of two or more converging and protected species is far less dis-
astrous; though when two species, equally distasteful, are involved,
the rarer of the two has the advantage, as Fritz Miiller has shown. His
lucid explanation is essentially as follows :
Suppose that the birds of a region have to destroy 1,200 butter-
flies of a distasteful species before it becomes recognized as such, and
that there exist in this region 2,000 individuals of species A and 10,000
of species B; then, if they are different in appearance, each will lose
1,200 individuals, but if they are deceptively alike, this loss will be di-
vided among them in proportion to their numbers, and A will lose 200
and B 1,000. A accordingly saves 1,000, or 50 per cent, of the total
number of individuals of the species, and B saves only 200, or 2 per cent.
Thus, while the relative numbers of the two species are as i to 5, the
relative advantage from their resemblance is as 25 to i.
If two or more distasteful species are equally numerous, their re-
semblance to one another brings nearly equal advantages. In cases of
this kind — and many are known — it is sometimes impossible to dis-
tinguish between model and mimic, as all the participants seem to
have converged toward a common protective appearance, through an
interchange of features — the "reciprocal mimicry" of Dr. Dixey.
Marshall argues, however, against this diaposematism, maintaining
that in the case of two participants in Miillerian mimicry the evolution
of the mimetic pattern has been in one direction only — toward the more
abundant species — any variations in the opposite direction being dis-
advantageous.
From this explanation, the superior value of Miillerian as compared
with Batesian mimicry is evident.
The fourth condition — that the imitators differ from the bulk of
their allies — holds true to such a degree that even the two sexes of the
same species may differ extremely in coloration, owing to the fact that
the female has assumed the likeness of some other and protected species.
ADAPTIVE COLORATION 205
The female of Papilio cenea, indeed, occurs (as was just mentioned)
under three varieties, which mimic respectively three entirely dis-
similar species oiDanais, and none of the females are anything like their
male in coloration.
The generally accepted explanation for these remarkable but numer-
ous cases in which the female alone is mimetic, is that the female, bur-
dened with eggs and consequently sluggish in flight and much exposed
to attack, is benefited by imitating a species which is immune; while
the male has had no such incentive — so to speak — to become mimetic.
Of course, there has been no conscious evolution of mimicry.
Wallace's fifth stipulation is important, but should read this way:
"The imitation, however minute, is but external and visible usually,
and never extends to internal characters which do not affect the exter-
nal appearance." For, as Poulton points out, the alertness of a beetle
which mimics a wasp, implies appropriate changes in the nervous and
muscular systems. In its intent, however, Wallace's rule holds good,
and by disregarding it some writers strain the theory of mimicry be-
yond reasonable limits. Some have said, for example,
that the resemblance between caddis flies and moths (^^f% gn^
is mimicry; when the fact is that this resemblance iT/^^Sl^
is not merely superficial but is deep-seated ; the entire | | \^
organization of Trichoptera shows that they are / N
closely related to Lepidoptera. This likeness P'^- 249.— a
^1 ^ • • -I . re •. J tettigomid, Myrme-
expresses, then, not mimicry, but ainmty and cophana fail ax,
parallel development. The same objection applies ^nt ""^ TwrcTnatui"!
to the assumed cases of mimicry within the limits length. Prom
of a single family, as between two genera of Heli- wattenwyl.
coniidas or between the chrysomelid genera Lema
and Diabrotica. The more nearly two species are related to each other,
the more probable it becomes that their similarity is due — not to mimi-
cry— but to their common ancestry.
On the other hand, the resemblance frequently occurs between
species of such different orders that it cannot be attributed to affinity.
Illustrations of this are the mimicry of the honey bee by the drone fly,
and the many other instances in which stinging Hymenoptera are
counterfeited by harmless flies or beetles. A tettigoniid of the Sudan
resembles an ant (Fig. 249), and the resemblance, by the way, is ob-
tained in a most remarkable manner. Upon the stout body of this
orthopteron the abdomen of an ant is delineated in black, the rest of
the body being light in color and inconspicuous by contrast with the
2o6 ENTOMOLOGY
black. Indeed the various means by which a superficial resemblance is
brought about between remotely related insects are often extraordinary.
Irrespective of affinity, insects of diverse orders may converge in
wholesale numbers toward a central protected form. The most com-
plete examples of this have been brought to light by Marshall and
Poulton, in their splendid work on the bionomics of South African
insects, in which is given, for instance, a colored plate showing how
closely six distasteful and dominant beetles of the genus Lycus are
imitated by almost forty species of other genera — a remarkable ex-
ample of convergence involving no less than eighteen families and
five orders, namely, Coleoptera, Hymenoptera, Hemiptera, Lepidoptera
and Diptera. Excepting a few unprotected, or Batesian, mimics (a fly
and two or three beetles), this association is one between species that
are already protected, by stings, bad tastes or other peculiarities.
In other words, here is Miillerian mimicry on an immense scale; and
if Miillerian mimicry is profitable when only two species are concerned,
what an enormous benefit it must be to each of forty participants !
Strength of the Theory. — Evidently the theory of mimicry rests
upon the assumption that the mimics, by virtue of their mimicry, are
specially protected from insectivorous foes. Formerly, however, there
was altogether too little evidence bearing upon the assumption itself,
though this was supported by such scattered observations as were
available. The oft-repeated assertion that this lack of evidence was
due simply to inattention to the subject, has been proved to be true
by the decisive results gained in the tropics by several competent
investigators who have been able to give the subject the requisite
amount of attention.
From his observations and experiments in India, Frank Finn con-
cludes:
"i. That there is a general appetite for butterflies among insec-
tivorous birds, even though they are rarely seen when wild to attack
them.
"2. That many, probably most, species dislike, if not intensely, at
any rate in comparison with other butterflies, the warningly-colored
Danainae, Acraa viola, Delias eucharis, and Papilio aristolochicB; ot
these the last being the most distasteful, and the Danainae the least so.
"3. That the mimics of these are at any rate relatively palatable,
and that the mimicry is commonly effectual under natural conditions.
''4. That each bird has separately to acquire its experience, and well
remembers what it has learned.
ADAPTR'E COLORATION 207
"That therefore on the whole, the theory of Wallace and Bates is
supported by the facts detailed in this and my former papers, so far as
they deal with birds (and with the one mammal used). Professor
Poulton's suggestion that animals may be forced by hunger to eat un-
palatable forms is also more than confirmed, as the unpalatable forms
were commonly eaten without the stimulus of actual hunger — generally,
also, I may add, without signs of dislike."
Though insects have many vertebrate and arthropod enemies, it is
probable that the evolution of mimetic resemblance, implying warning
coloration, has been brought about chiefly by insectivorous birds.
Neglecting papers of minor importance, we may pass at once to the
most important contribution upon this subject — the voluminous work
of Marshall and Poulton upon mimicry and warning colors in South
African insects. These investigators have found that birds are to be
counted as the principal enemies of butterflies; that the Danainae and
Acraeinse, which are noted as models, are particularly immune from de-
struction, while unprotected forms suffer; and that mimicking, though
palatable, species share the freedom of their models. The same is true
of beetles, of which Coccinellidse, Malacodermidse (notably Lycus)
Cantharidae and many Chrysomelidae serve as models for many other
Coleoptera, being "conspicuous and constantly refused by insect-
eaters." In short, the splendid work of Marshall and Poulton tends to
place the theory of Batesian and Miillerian mimicry upon a substantial
foundation of observational and experirnental evidence.
In regard to the important question — do birds avoid unpalatable
insects instinctively or only as the result of experience — the evidence is
all one way. Several investigators, including Lloyd Morgan, have
found that newly-hatched birds have no instinctive aversions as regards
food, but test everything, and (except for some little parental guidance)
are obliged to learn for themselves what is good to eat and what is not.
This experimental evidence that the discrimination of food by birds is
due solely to experience, was evidently highly necessary to place the
theory of mimicry — especially the Miillerian theory — upon a sound
basis.
Though butterflies as a group are much subject to the attacks of
birds in the tropics, it has been asserted that butterflies in temperate
regions are as a whole almost exempt from the attacks of birds, and that
consequently the mimicry of the monarch (Fig. 247) by the viceroy is
of no advantage. In answer to this assertion Marshall has pubhshed a
long list of references showing that butterflies are attacked by birds
2o8 ENTOMOLOGY
more commonly than has been generally supposed. At the same time
there is no proof that the viceroy profits at present by its mimetic
pattern, though it may have done so in the past. In any event, the
departure of archippus from its congeners toward one of the Danainae — a
famous group of "models" in the tropics — is unintelligible except as an
instance of mimicry.
Granting that mimicry is upon the whole advantageous, it becomes
important to learn just how far the advantage extends; and we find that
mimicry is not of universal effectiveness. Even the highly protected
Heliconiinas and Danainse are food for some predaceous insects. In
this country, as Judd has observed, the drone-fly {Eristalis tenax), which
mimics the honey bee, is eaten by the kingbird and the phcebe; the
kingbird, indeed, eats the honey bee itself, but is said to pick out the
drones; chickens also discriminate between drones and workers, eating
the former and avoiding the latter. Bumblebees and wasps, imitated
by many other insects, are themselves eaten by the kingbird, catbird
and several other birds, though it is not known whether the stingless
males of these are singled out or not. Such facts as these do not discredit
the general theory of mimicry but point out its limits.
Evolution of Mimicry. — Natural selection gives an adequate ex-
planation of the evolution of a mimetic pattern. Before accepting this
explanation, however, we must inquire: (i) What were the first stages
in the development of a mimetic pattern? (2) What evidence is there
that every step in this development was vitally useful, as the theory de-
mands that it should be? These pertinent questions have been
answered by Darwin, Wallace, Miiller, Dixey and several other
authorities.
The incipient mimic must have possessed, to begin with, colors or
patterns that were capable of mimetic development; evidently the raw
material must have been present. Now Miiller and Dixey in particular
have called attention to the fact that many pierids have at least touches
of the reds, yellows and other colors that are so conspicuous in the heli-
coniids. More than this, however, Dixey has demonstrated — as appears
clearly from his colored figures — a complete and gradual transition from
a typical non-mimetic pierid, Pieris locusta, to the mimetic pierid
Mylothris pyrrha, the female of which imitates Heliconius numata. He
traces the transition chiefly through the males of several pierid species —
for the males, though for the most part white (the typical pierid color),
"show on the under surface, though in varying degrees, an approach
towards the Heliconiine pattern that is so completely imitated by their
ADAPTIVE COLORATION 209
mates. These partially developed features on the under surface of the
males enable us to trace the history of the growth of the mimetic
pattern." Starting from Pieris locusta, it is an easy step to Mylothris
lypera, thence to M. lorena, and from thtfe to the mimetic M. pyrrha.
"Granted a beginning, however small, such as the basal red touches in
the normal Pierines, an elaborate and practically perfect mimetic
pattern may be evolved therefrom by simple and easy stages."
Furthermore (in answer to the second question), it does not tax the
imagination to admit that any one of these color patterns has — at least
occasionally — been sufficiently suggestive of the heliconiid type to pre-
serve the hfe of its possessor; especially when both bird and insect were
on the wing and perhaps some distance apart, when even a momentary
flash of red or yellow from a pierid might be enough to save it from
attack.
It is highly desirable, of course, that this plausible explanation
should be tested as far as possible by observations in the field and by
experiments as well.
Mimicry and Mendelism. — The weight of evidence is at present
vastly in favor of the theory of mimicry as against any other explanation
of the facts, even though the theory is sometimes stretched to impossible
limits by some of its enthusiastic adherents. The only opposing opinion
that has sufficient plausibility to demand much consideration as yet
is that of Punnett.
In India and Ceylon the butterfly Papilio polytes has in addition to
the normal female a second form of female which mimics P. aristolochia
and a third which imitates P. hector; polytes being palatable to birds
and its two models unpalatable.
This case, described by Wallace more than fifty years ago, is one of
the classic examples of mimicry. Punnett holds, however, that these
resemblances are of no practical value and that natural selection htis
played no part in the formation of these polymorphic forms and suggests
that Mendehsm offers a better explanation of the phenomenon— a
suggestion that should be tested experimentally.
Adaptive Colors in General.— Several classes of adaptive colors
have been discriminated and defined by Poulton, whose classification,
necessarily somewhat arbitrary but nevertheless very useful, is given
below, in its abridged form.
ENTOMOLOGY
III.
APATETIC COLORS.— Colors resembling some part of the environment or the
appearance of another species.
A. Cryptic Colors. — Protective and Aggressive Resemblances.
1. Procryptic colors. — Protective Resemblances. — Concealment as a pro-
tection against enemies. Example: Kallima butterfly.
2. Anticryptic colors. — Aggressive Resemblances. — Concealment in order to
facilitate attack. Example: Mantids with leaf-like appendages.
B. PsEUDOSEMATic COLORS. — False warning and signalling colors.
1. Pseudaposematic colors.- — Protective Mimicry. Example: Bee-like fly.
2. Psendepisematic colors. — Aggressive INIimicry and Alluring Coloration.
Examples: Volucella, resembling bees (Fig. 250); Flower-like mantid.
SEMATIC COLORS.— Warning and SignalUng Colors.
1. Aposematic colors. — Warning Colors. — Examples: Gaudy colors of stinging
insects.
2. Episematic colors. — Recognition Markings.
EPIGAMIC COLORS.— Colors Displayed in Courtship.
Such of these classes as have not already been discussed need brief
reference.
Aggressive Resemblances. — The resemblance of a carnivorous
animal to its surroundings may not only be protective but may also
Fig. 250. — Aggressive mimicry. On the left, a bee, Bombus maslrucatus; on the right,
fly, Volucella bombylans. Natural size.
enable it to approach its prey undetected, as in the case of the polar bear
or the tiger. Among insects, however, the occurrence of aggressive
resemblance is rather doubtful, even in the case of the leaf-Hke mantids.
Aggressive Mimicry. — Under this head are placed those cases in
which one species mimics another to which it is hostile. The best
known instance is furnished by European flies of the genus Volucella ^
whose larvae feed upon those of bumblebees and wasps. The flies bear
a close resemblance to the bees, owing to which it is supposed that the
former are able to enter the nests of the latter and lay their eggs.
Alluring Coloration. — The best example of this phenomenon is
afforded by an Indian mantid, Gongylus gongyloides, which resembles so
perfectly the brightly colored flowers among which it hides that insects
actually fly straight into its clutches.
ADAPTIVE COLORATION 211
Recognition Markings.— Though these are apparently important
among mammals and birds, as enabling individuals of the same species
quickly to recognize and follow one another, no special markings for
this purpose are known to occur among insects, not excepting the gre-
garious migrant species, such as Anosia plexippus and the Rocky
Mountain locust.
Epigamic Colors. — Among birds, frequently, the bright colors of
the male are displayed during courtship, and their evolution has been
attributed by Darwin and many of his followers to sexual selection — a
highly debatable subject. Among insects, however, no such phenome-
non has been found; whenever the two sexes differ in coloration the
difference does not appear to faciHtate the recognition of even one sex
by the other.
Evolution of Adaptive Coloration. — Natural selection is the only
theory of any consequence that explains the highly involved phenomena
oi adaptive coloration. Against such vague and unsupported theories
as the action of food, climate, laws of growth or sexual selection, natural
selection alone accounts for the multitudinous and intricate correlations
of color, pattern, form, attitude, movement, place, time, etc., that are
necessary to the development of a perfect case of protective resemblance
or mimicry. Natural selection cannot, of course, originate colors or any
other characters, its action being restricted to the preservation and
accumulation of such advantageous variations as may arise, from what-
ever causes. As Poulton says, the vast body of facts, utterly meaning-
less under any other theory, become at once intelligible as they fall
harmoniously into place under the principle of natural selection, to
which, indeed, they yield the finest kind of support.
CHAPTER VII
INSECTS IN RELATION TO PLANTS
Insects, in common with other animals, depend for food primarily
upon the plant world. No other animals, however, sustain such intimate
and complex relations to plants as insects do. The more luxuriant and
varied the flora, the more abundant and diversified is its accompanying
insect fauna.
Not only have insects become profoundly modified for using all kinds
and all parts of plants for food and shelter, but plants themselves have
been modified to no small extent in relation to insects, as appears in their
protective devices against unwelcome insects, in the curious formations
known as "galls," the various insectivorous plants, and especially the
omnipresent and often intricate floral adaptations for cross-polhnation
through the agency of insect visitors. .Though insects have laid plants
under contribution, the latter have not only vigorously sustained the
attack but have even pressed the enemy into their own service, as it were.
Numerical Relations. — The number of insect species supported by
one kind of plant is seldom small and often surprisingly large. The
poison ivy {Rhus toxicodendron) is almost exempt from attack, though
even this plant is eaten by a leaf-mining caterpillar, two pyralid larvae
and the larva of a scolytid beetle (Schwarz, Dyar) . Horse-chestnut
and buckeye have perhaps a dozen species at most; elm has eighty;
birches have over one hundred, and so have maples; pines are known to
harbor 170 species and may jdeld as many more; while our oaks sustain
certainly 500 species of insects and probably twice as many. Turn-
ing to cultivated plants, the clover is affected, directly or indirectly, by
about 200 species, including predaceous insects, parasites, and flower-
visitors. Clover grows so vigorously that it is able to withstand a great
deal of injury from insects. Corn is attacked by about 200 species, of
which 50 do notable injury and some 20 are pests. Apple insects num-
ber some 400 species.
Not uncommonly, an insect is restricted to a single species of plant.
Thus the caterpillar of Heodes hypophlceas feeds only on sorrel {Rumex
acetosella), so far as is known. The chrysomelid Chrysochus auratus
appears to be limited to Indian hemp {Apocynum androscemifolium) and
INSECTS IN RELATION TO PLANTS
213
to milkweed (Asclepias). In many instances an insect feeds indiffer-
ently upon several species of plants provided these have certain attri-
butes in common. Thus Argynnis cybele, aphrodite and atlantis eat the
leaves of various species of violets, and the Colorado potato beetle eats
different species of Solanum. Papilio thoas feeds upon orange, prickly
ash and other Rutaceae. Anosia plexippus eats the various species of
Asclepias and also Apocynum androscemifolium; while Chrysochus also
is Hmited to these two genera of plants, as was said. These plants agree
in having a milky juice; in fact the two genera are rather nearly related
botanically. The common cabbage butterfly {Pieris rapes) though con-
fined for the most part to Cruciferae, such as cabbage, mustard, turnip,
radish, horse-radish, etc., often devel- a
ops upon Tropceolum, which belongs to
Geraniaceae; all its food plants, how-
ever, have a pungent odor, which is
probably the stimulus to oviposition.
Most phytophagous insects range
over many food plants. The cecropia
caterpillar has more than sixty of
these, representing thirty-one genera
and eighteen orders of plants; and the
tarnished plant bug [Lygus pratensis)
feeds indifferently on all sorts of herb-
age, as does also the caterpillar of Dia-
crisia virginica. Many of the insects
of apple, pear, quince, plum, peach,
and other plants of the family Rosaceae
occur also on wild plants of the same
family; and the worst of our corn and wheat insects have come from
wild grasses. As regards number of food plants, the gipsy moth "holds
the record," for its caterpillar will eat almost any plant. In Massachu-
setts, according to Forbush and Fernald, it fed in the field upon 78
species of plants, in captivity upon 458 species (30 under stress of
hunger, the rest freely), and refused only 19 species, most of which
(such as larkspur and red pepper) had poisonous or pungent juices,
or were otherwise unsuitable as food. The migratory locust is noto-
riously omnivorous, and perhaps eats even more kinds of plants than
the gipsy moth.
Galls.— Most of the conspicuous plant outgrowths known as "galls"
are made by insects, though many of the smaller plant galls are made
Pig. 251. — Holcaspis globulus. A,
galls on oak, natural size; B, the gall-
maker, twice natural length.
214
ENTOMOLOGY
by mites (Acarina) and a few plant excrescences are due to nematode
worms and to fungi.
Among insects, Cynipidae (Hymenoptera) are pre-eminent as gall-
FiG. 252
of Holcaspis duricoria, on oak. Natural size.
makers and next to these, Itonididae (Diptera), Aphididae and
Psyllidae (Hemiptera) ; a few gall-insects occur among Tenthredinidae
(Hymenoptera) and Trypetidae (Diptera),
and one or two among Coleoptera and
Lepidoptera.
Cynipidae affect the oaks (Figs. 251,
252) far more often than any other plants,
though not a few species select the wild
rose. Itonidid galls occur on a great
variety of plants, and those of aphids on
elm (Fig. 253), poplar, and many other
plants; while psyllid galls are most fre-
quent on hackberry. The galls may occur
anywhere on a plant, from the roots to
the flowers or seeds, though each gall-
maker always works on the same part
of its plant, — root, stem, bud, leaf, leaf-
vein, flower, seed, etc.
Galls present innumerable forms, but
the form and situation of a gall are
usually characteristic, so that it is often
possible to classify galls as species even before the gall-maker is known.
Gall-Making. — The female simply lays the egg on the epidermis, or
else punctures the plant and deposits an egg in or near the cambium, or
any other tissue capable of growth; the egg hatches and the surrounding
plant tissue is stimulated to grow rapidly and abnormally into a gall,
Pig. 253. — Cockscomb gall of
Colopha ulmicola, on elm. Slightly
reduced.
INSECTS IN RELATION TO PLANTS 215
which serves as food for the larva; this transforms within the gall and
escapes as a winged insect. The physiology of gall-formation is far
from being understood. It has been found that the mechanical irrita-
tion from the ovipositor is not the initial stimulus to the development
of a gall; neither is the fluid which is injected by the female during
oviposition, this fluid being probably a lubricant; if the egg is removed,
the gall does not appear. Ordinarily the gall does not begin to grow
until the egg has hatched, and then the gall grows along with the larva;
exceptions to this are found in some Tenthredinidae in which the egg it-
self increases in volume, when the gall may grow with the egg. It
appears that the larva exudes some fluid which acts upon the proto-
plasm of certain plant cells (the cambium and other cells capable of
further growth and multiplication) in such a way as to stimulate their
increase in size and number. The following observations on this subject
by A. Cosens are important. The cells of the plant that immediately
surround the larva are known as nutritive cells. In Cynipidae the
larva gradually withdraws the contents of these cells, by means of the
mouth and not by absorption, and the cells gradually collapse. The
proportion of sugar to starch decreases from the inside of the nutritive
zone (nearest the larva) to the outside. This is owing to an enzyme
that changes starch into sugar, the source of this enzyme being probably
a pair of salivary glands that open externally on each side just below the
mouth of the larva. The larva by accelerating the rate of change from
starch to sugar renders available to the plant more food than usual and
therefore stimulates the activity of the protoplasm toward greater cell-
growth and more rapid cell-reproduction. Thus the gall as well as the
larva draws food from the nutritive zone.
Why the gall should have a distinctive, or specific, form, it is not yet
known. There is no evidence that the form is of any adaptive impor-
tance, and the subject probably admits of a purely mechanical explana-
tion. One factor in determining the form of the gall is the direction in
which the stimulus is apphed; a spherical cynipid gall arising when the
influence is about equally distributed in all directions (Cosens) .
Gall Insects. — The study of gall insects is in many respects difficult.
It is not at all certain that an insect which emerges from a gall is the
species that made it; for many species, even of Cynipidae, make no galls
themselves but lay their eggs in galls made by other species. Such
guest-insects are termed inquilines. Furthermore, both gall-makers
and inquihnes are attacked by parasitic Hymenoptera, making the in-
terrelations of these insects hard to determine. Many species of insects
2l6 ENTOMOLOGY
feed upon the substance of galls; thus Sharp speaks of as many as thirty
different kinds of insects, belonging to almost all the orders, as having
been reared from a single species of gall.
Parthenogenesis and Alternation of Generations. — Parthenogenesis
has long been known to occur among Cynipidae. It has repeatedly
been found that of thousands of insects emerging from galls of the
same kind, all were females. In one such instance the females were
induced by Adler to lay eggs on potted oaks, when it was found that the
resulting galls were quite unlike the original ones, and produced both
sexes of an insect which had up to that time been regarded as another
species. Besides parthenogenesis and this alternation of generations,
many other complications occur, making the study of gall-insects an
intricate and highly interesting subject.
Plant-Enemies of Insects. — Most of the flowering plants are com-
paratively helpless against the attacks of insects, though there are many
devices which preveint "unwelcome" insects from entering flowers, for
instance the sticky calyx of the catchfly {Silene virginica), which
entangles ants and small flies. A few plants, however, actually feed
upon insects themselves. Thus the species of Drosera, as described in
Darwin's classic volume on insectivorous plants, have specialized leaves
for the purpose of catching insects. The stout hairs of these leaves end
each in a globular knob, which secretes a sticky fluid. When a fly
ahghts on one of these leaves the hairs bend over and hold the insect;
then a fluid analogous to the gastric juice of the human stomach exudes,
digests the albuminoid substances of the insect and these are absorbed
into the tissues of the leaf; after which the tentacles unfold and are
ready for the next insect visitor. The Venus's flytrap is another well
known example; the trap, formed from the terminal portion of a leaf,
consists of two valves, each of which bears three trigger-like bristles,
and when these are touched by an insect the valves snap together and
frequently imprison the insect, which is eventually digested, as before.
In the common pitcher-plants, the pitcher, fashioned from a leaf, is lined
with downward pointing bristles, which allow an insect to enter but
prevent its escape. The bottom of the pitcher contains water, in
which ma^ be found the remains of a great variety of insects which
have drowned. There are even nectar glands and conspicuous colors,
presumably to attract insects into these traps, where their decomposi-
tion products are more or less useful to the plant. In Pinguicula the
margin of a leaf rolls over and envelops insects that have been caught
by the glandular hairs of the upper surface of the leaf, a copious secretion
INSECTS IN RELATION TO PLANTS
217
digests the softer portions of the insects, and the dissolved nitrogenous
matter is absorbed into the plant. Utricularia has little bladders which
entrap small aquatic insects. These plants are only partially dependent
on insect-food, however, for they all possess chlorophyll.
Bacteria cause epidemic diseases among insects, as in the flacherie
of the silkworm; and fungi of a few groups are spe-
cially adapted to develop in the bodies of living fl
insects.
Those who rear insects know how frequently
caterpillars and other larvae are destroyed by fungi
that give the insects a powdered appearance. These
fungi, referred to the genus Isaria, are in some cases
known to be asexual stages of forms of Cordyceps,
which forms appear from the bodies of various larvae,
pupae and imagines as long, conspicuous, fructifying
sprouts (Fig. 254).
The chief fungous parasites of insects belong to
the large family Entomophthoracese, represented by
the common Empusa nmsccB (Fig. 255) which affects
various flies. In autumn, especially in warm moist
weather, the common house fly may often be seen
in a dead or dying condition, sticking to a window-
pane, its abdomen distended and presenting alter-
nate black and white bands, while around the fly
at a little distance is a white powdery ring, or halo.
The white intersegmental bands are made by threads
of the fungus just named, and the white halo by
countless asexual spores known as conidia, which
have been forcibly discharged from the swollen
threads that bore them (Fig. 255) by pressure, result-
ing probably from the absorption of moisture. These
spores, ejected in all directions, may infect another
fly upon contact and produce a growth of fungus
threads, or hyphcE, in its body. The fungus may be propagated also
by means of resting spores, as found by Thaxter, our authority on the
fungi of insects.
Empusa aphidis is very common on plant lice and is an important
check upon their multipHcation. Aphids killed by this fungus are
found cUnging to their food plant, with the body swollen and discolored.
Empusa grylli attacks crickets, grasshoppers, caterpillars and other
Pig. 254. — Fruc-
tifying sprouts . of
a fungus, Cordyceps
ravenelit, a r i s'i n g
from the body of a
white grub, Lachno-
sterna. Slightly
reduce d. — A f t e r
Riley.
2l8
ENTOMOLOGY
forms. Curiously enough, grasshoppers affected by this fungus almost
always crawl to the top of some plant and die in this conspicuous position.
Sporotrichum, a genus of hyphomycetous fungi, affects a great
variety of insects, spreading within the body of the host and at length
emerging to form on the body of the insect a dense white felt-like
covering, this consisting chiefly of myriads of spores, by means of which
healthy insects may become infected. Under favorable conditions,
especially in moist seasons, contagious fungous diseases constitute one
of the most important checks upon the increase of insects and are
therefore of vast economic importance. Thus the termination (in i^
Fig. 255. — Empusa mtisccB, the common fly-fungus. A, house fly (Musca domeslica),
surrounded by fungus spores (conidia) ; B, group of conidiophores showing conidia in
several stages of development; C, basidium [h) bearing conidium (c) before discharge.
B and C after Th.\xter.
of a disastrous outbreak of the chinch bug in Illinois and neighboring
states "was apparently due chiefly, if not altogether, to parasitism by
fungi." Artificial cultures of the common Sporotrichum glohulijerum
have been used extensively as a means of spreading infection among
chinch bugs and grasshoppers, with, however, but moderate success.
Transmission of Diseases of Plants.— Not a few bacterial and fun-
gous diseases of plants are known to be transmitted by insects. M. B.
Waite proved experimentally that the bacillus causing fire blight of
pear, apple and other pomaceous trees is carried by honey bees and
other insects from flower to flower, multiplies in the nectar, and enters the
host plant. Bees, wasps and flies obtain the bacilli from the exudation
from old cankers and carry the organisms either to blossoms or to young
INSECTS IN RELATION TO PLANTS 219
growing shoots. Other investigators have found that apple aphids,
leafhoppers, the tarnished plant bug {Lygus pratensis) and the shot-hole
borer {Scolytus rugulosus) are also responsible for the inoculation of
fruit trees with the bacilli of blight.
Dr. E. F. Smith demonstrated that cucurbit wilt is spread, probably
exclusively, by insects, particularly the striped and the twelve-spotted
cucumber beetles {Diahrotica vittata and D. duodecim punctata, respect-
ively), which introduce the bacilli of the disease into the plants as they
feed. Some of the beetles carry the bacillus over winter, in the alimen-
tary tract, and infect young plants with the wilt in spring.
The spores of the fungous disease known as brown rot of peach and
plum are probably carried by bees, wasps and certain other insects,
and introduced into wounds in the fruits made by themselves or other
insects. The plum curculio almost certainly leaves these spores in
punctures that it makes.
Cankers of Leptosphceria on apple bark occur around the oviposition
wounds made by tree-crickets {(Ecanthus), and it has been shown experi-
mentally that these insects convey the spores of the disease both
externally and internally and inoculate them into the host plant.
Typical cankers on apple branches have been obtained artficially by
inoculation with feces of tree-crickets fed on spores of the disease.
The mosaic diseases of cucumber, potato and tobacco are trans-
mitted by plant lice. The spores of bitter rot of apples are conveyed
from decaying apples to sound fruits by pomace flies (Drosophila).
Insects in Relation to Flowers. — Among the most marvelous phe-
nomena known to the biologist are the innumerable and complex
adaptations by means of which flowers secure cross pollination through
the agency of insect visitors. Cross fertilization is actually a necessity
for the continued vigor and fertility of flowering plants, and while some
of them are adapted for cross pollination by wind or water, the majority
of flowering plants exhibit profound modifications of floral structure for
compelling insects (and a few other animals, as birds or snails) to carry
pollen from one flower to another. ' In general, the conspicuous colors
of flowers are for the purpose of attracting insects, as are also the odors
of flowers. Night-blooming flowers are often white or yellow and as a
rule strongly scented. Colors and odors, however, are simply indica-
tions to insects that edible nectar or pollen is at hand. Such is the
usual statement, and it is indeed probable that insects actually do asso-
ciate color and nectar, even though they will fly to bits of colored paper
almost as readily as they will to flowers of the same colors. It is not
2 20 ENTOMOLOGY
to be supposed, however, that insects feahze that they confer any benefit
upon the plant in the flowers of which they find food. At any rate,
most flowers are so constructed that certain insects cannot get the
nectar or pollen without carrying some pollen away, and cannot enter
the next flower of the same kind without leaving some of this pollen
upon the stigma of that flower. Take the iris, for example, which is
admirably adapted for pollination by a few bees and flies.
Iris. — In the common blue-flag {Iris versicolor, Fig. 256) each of the
Fig. 256. — Bumblebee (Bo7nbiis) entering flower of blue-flag (Iris versicolor). Slightly
reduced.
three drooping sepals forms the floor of an arched passageway leading
to the nectar. Over the entrance and pointing outward is a movable
lip (Fig. 257, /), the outer surface of which is stigmatic. An entering
bee hits and bends down the free edge of this lip, which scrapes pollen
from the back of the insect and then springs back into place. Within
the passage, the hairy back of the bee rubs against an overhanging
anther (an) and becomes powdered with grains of pollen as the insect
pushes down towards the nectar. As the bee backs out of the passage
INSECTS IN RELATION TO PLANTS
it encounters the guardian lip again, but as this side of the lip cannot
receive pollen, immediate close pollination is prevented. Of course,
it is possible for bees to enter another part of the same flower or another
flower of the same plant, but as a matter of fact, they habitually fly
away to another plant; moreover, as Darwin found, foreign pollen is
prepotent over pollen from the same flower. It may be added that
bees and other poUenizing insects ordi-
narily visit in succession several flowers
of the same kind.
Orchids. — The orchids, with their
fantastic forms, are really elaborate
traps to insure cross pollination. In
some orchids {Hahenaria and others)
the nectar, lying at the bottom of a
long tube, is accessible only to the long-
tongued Sphingidae. While probing for
the nectar, a sphinx moth brings each
eye against a sticky disk to which a
pollen mass is attached, and flies away
carrying the mass on its eye. Then
these pollinia bend down on their stalks
in such a way that when the moth
thrusts its head into the next flower
they are in the proper position to
encounter and adhere to the stigma.
The orchid Angr cecum sesquipedale, of
Madagascar, has a nectary tube more
than eleven inches long, from which Darwin inferred the existence of a
sphinx moth with a tongue equally long.
Milkweed. — The various milkweeds are fascinating subjects to the
student of the interrelations of flowers and insects. The flowers, like
those of orchids, are remarkably formed with reference to cross pollina-
tion by insects. As a honey bee or other insect crawls over the flowers
(Fig. 258, yl) to get the nectar, its legs slip in between the pecuUar nec-
tariferous Jwods situated in front of each anther. As a leg is drawn up-
ward one of its claws, hairs, or spines frequently catches in a V-shaped
fissure (/, Fig. 258, B) and is guided along a sHfto a notched disk, or cor-
puscle (Fig. 258, C, d). This disk cHngs to the leg of the insect, which
carries off by means of the disk a pair of pollen masses, or pollinia (Fig.
258, C). When first removed from their enclosing pockets, or anthers,
Fig. 257. — Section to illustrate
cross pollination of Iris, an, anther;
I, stigmatic lip; n, nectary; s, sepal.
222 ENTOMOLOGY
these thin spatulate pollinia lie each pair in the same plane, but in a few
seconds the two pollinia twist on their stalks and come face to face in
such a way that one of them can be easily introduced into the stigmatic
chamber of a new flower visited by the insect. Then the struggles of the
insect ordinarily break the stem, or retinaculum, of the poUinium and
free the insect. Often, however, the insect loses a leg or else is per-
manently entrapped, particularly in the case of such large-flowered
milkweeds as Asclepias cornuti, which often captures bees, flies and
moths of considerable size. Pollination is accomplished by a great
Fig. 258. — Structure of milkweed flower (Asclepias incarnata) with reference to cross
pollination. A, a single flower; c, corolla; h, hood; B, external aspect of fissure (/) leading
up to disk and also into stigmatic chamber; h, hood; C, pollinia; d, disk. Enlarged.
variety of insects, chiefly Hymenoptera, Diptera, Lepidoptera and
Coleoptera. These insects when collected about milkweed flowers
usually display the pollinia dangUng from their legs, as in Fig. 259.
The details of pollination may be gathered by a close observer from
observations in the field and may be demonstrated to perfection by using
a detached leg of an insect and dragging it upward between two of the
hoods of a flower; first to remove the pair of pollinia and then again
to introduce one of them into an empty stigmatic chamber.
Yucca. — An extraordinary example of the interdependence of plants
and insects was made known by Riley, whose detailed account is here
summarized. The yuccas of the southern United States and Mexico
are among the few plants that depend for pollination each upon a single
species of insect. The pollen of Yucca filamentosa cannot be introduced
into the stigmatic tube of the flower without the help of a Httle white
INSECTS IN RELATION TO PLANTS
Fig. 259. — A wasp, Spliex ichneu-
mon e a, with pollinia of milkweed
attached to its legs. Slightly enlarged.
tineid moth, Proniiha yuccasella, the female of which pollenizes the flower
and lays eggs among the ovules, that her larvae may feed upon the young
seeds. While the male has no unusual structural peculiarities, the
female is adapted for her special work
by modifications which are unique
among Lepidoptera, namely, a pair
of prehensile and spinous maxillary
"tentacles" (Fig. 260, A) and a long
protrusible ovipositor {B) which com-
bines in itself the functions of a lance
and a saw.
The female begins to work soon
after dark, and will continue her opera-
tions even in the light of a lantern.
Clinging to a stamen (Fig. 261) she
scrapes off pollen with her palpi and
shapes it into a pellet by using the front legs. After gathering pollen
from several flowers she flies to another flower, as a rule, thrusts her
long flexible ovipositor into the ovary (Fig. 262) and lays a slender egg
alongside seven or eight of
the ovules. After laying one
or more eggs she ascends the
pistil and actually thrusts
pollen into the stigmatic tube
and pushes it in firmly. The
ovules develop into seeds,
some of which are consumed
by the larvae, though plenty
are left to perpetuate the
plant itself. Three species
of Pronuha are known, each
restricted to particular
species of Yucca. Riley says
that Yucca never produces
seed where Pronuba does not
occur or where she is excluded
artificially, and that artificial
pollination is rarely so suc-
FiG. 260. — Pronuha yuccasella. A, maxillary
tentacle and palpus; B, ovipositor. — After Riley.
Figures 260-262 are republished from the Third
Report of the Missouri Botanical Garden, by
permission.
cessful as the normal method.
Why does the insect do this?
The little nectar secreted at the base
224
ENTOMOLOGY
of the pistil appears to be of no consequence, at present, and the stig-
matic fluid is not nectarian; indeed, the tongue of Pronuha, used in
clinging to the stamen, seems to have lost partially or entirely its
sucking power, and the alimentary canal is regarded as functionless.
Ordinarily it is the flower which has become adapted to the insect,
which is enticed by means of pollen or nectar, but here is a flower which —
though entomophilous in general structure — has apparently adapted
itself in no way to the single insect upon which it is dependent for the
continuance of its existence. More than this, the insect not only labors
Fig. 261. — Pronuha yuccasella,
female, gathering pollen from anthers
of Yucca. Enlarged.
Fig. 262.
-Pronuha moth ovipositing in flower of
Yucca. Slightly reduced.
without compensation in the way of food, but has even become highly
modified with reference to the needs of the plant, — its special modifica-
tions being unparalleled among insects with the exception of bees, and
being more puzzHng than the more extensive adaptations of the bees
when we take into consideration the impersonal nature of the operations
of Pronuha. Further investigation may render these extraordinary
interrelations more intelligible than they are at present.
The bogus Yucca moth {Prodoxus quinquepunctella) closely resembles
and associates with Pronuha but oviposits in the flower stalks of Yucca
and has none of the special adaptive structures found in Pronuha.
As regards floral adaptations, these examples are sufi&cient for pres-
ent purposes; many others have been described by the botanist; in fact,
the adaptations for cross pollination by insects are as varied as the
flowers themselves.
INSECTS IN RELATION TO PLANTS
225
Insect Pollenizers.— The great majority of entomophilous flowers
are pollenized by bees of various kinds; the apple, pear, blackberry,
raspberry and many other rosaceous plants depend chiefly upon the
honey bee, while clover cannot set seed without the aid of bumblebees
or honey bees, assisted by wild bees such as Tetralonia and Melissodes.
LiUes and orchids frequently employ butterflies and moths, as well as
bees, and the milkweed is adapted in a remarkable manner for pollination
by butterflies, moths and some wasps, as was described. Honeysuckle,
lilac, azalea, tobacco. Petunia, Datura and many other strongly scented
and conspicuous nocturnal flowers attract for their own uses the long-
tonged sphinx moths (Fig. 263) ; the evening primrose, like milkweed,
is a favorite of noctuid moths.
UmbeUiferous plants are pollen-
ized chiefly by various flies, but
also by bees and wasps. Pond
lilies, golden rod and some other
flowers are pollenized largely by
beetles, though the flowers exhibit
no special modifications in relation
to these particular insects. It is
noteworthy that polhnation is per-
formed only by the more highly
organized insects, the bees head-
ing the list.
Of all the insects that haunt the
same flower, it frequently happens
that only a few are of any use to the
flower itself; many come for pollen
only; many secure the nectar illegitimately; thus bumblebees puncture
the nectaries of columbine, snapdragon and trumpet creeper from the
outside, and wasps of the genus Odynerus cut through the corolla of
Pentestemon Icevigatus, making a hole opposite each nectary; then there
are the many insects that devour the floral organs, and the insects which
are predaceous or parasitic upon the others. In the Iris, according to
Needham, two small bees {Clisodon terminalis and Osmia distincta) are
the most important pollenizers, and next to them a few syrphid flies,
while bumblebees also are of some importance. The beetle Trichius
piger and several small flies obtain pollen without assisting the plant,
and Pamphila, Eudatnus, Chrysophanus and some other butterflies
succeed after many trials in stealing the nectar from the outside (Fig.
Pig. 263. — Protoparce sexla visiting flower
of Petunia. Reduced.
2 26 ENTOMOLOGY
264). A weevil {Mononychus vulpeculus) punctures the nectary, and
the flowing nectar then attracts a great variety of insects. Grass-
hoppers and caterpillars eat the flowers, an ortalid fly destroys the buds,
and several parasitic or predaceous insects haunt the plant ; in all, more
than sixty species of insects are concerned in one way or another with
the Iris.
Fig. 264. — A butterfly, Polites peckius, stealing nectar from a flower of Iris versicolor.
Slightly reduced.
Modifications of Insects with Reference to Flowers. — While the
manifold and exquisite adaptations of the flower for cross polhnation
have engaged universal attention, very little has been recorded con-
cerning the adaptations of insects in relation to flowers. In fact,
the adaptation is largely one-sided; flowers have become adjusted to
the structure of insects as a matter of vital necessity — to put it that
way — while insects have had no such urgent need — so to speak — in rela-
tion to floral structure. They have been influenced by floral structure to
some extent however, and in some cases to a very great extent, as ap-
pears from their structural and physiological adaptations for gathering
and using pollen and nectar.
INSECTS IN RELATION TO PLANTS
227
Among mandibulate insects, beetles and caterpillars that eat the
floral envelopes show no special modifications for this purpose; pollen-
feeding beetles, however, usually have the mouth parts densely clothed
with hairs, as in Euphoria (Fig. 265). In suctorial insects, the mouth
parts are frequently formed with reference to floral structure; this is
the case in many butterflies and particularly in Sphingidae, in which the
length of the tongue bears a direct relation to the depth of the nectary
in the flowers that they visit. According to MiiUer, the mouth parts of
Syrphida?, Stratyomyiidae and Muscidae are specially adapted for feed-
FiG. 265. — A, right mandible; B, right maxilla; C, hypo-
pharynx, of a pollen-eating beetle. Euphoria inda. Enlarged.
(The mandibles are remarkable in being two-lobed.)
Fig. 266. — Pollen-gath-
ering hair from a worker
honey bee, with a pollen
grain attached. Greatly
magnified.
ing on pollen. In Apidae, the tongue as compared with that of other
Hymenoptera, is exceptionally long, enabling the insect to reach deep
into a flower, and is exquisitely specialized (Fig. 129) for lapping up
and sucking in nectar.
Pollen-gathering flies and bees collect pollen in the hairs of the body
or the legs ; these hairs, especially dense and often twisted or branched
(Figs. 266, 91) to hold the pollen, do not occur on other than pollen-
gathering species of insects. Caudell found that out of 200 species of
Hymenoptera only 23 species had branched hairs and that these species
belonged without exception to the pollen-gathering group Anthophila,
no representative of which was found without such hairs. Similar
228
ENTOMOLOGY
branched hairs occur also on the flower-frequenting Bombyliidae and
Syrphidae.
The most extensive modifications in relation to flowers are found in
Fronuba, as already described, and above all in Apidae, especially the
honey bee.
Honey Bee.- — The thorax and abdomen and the bases of the legs
are clothed with flexible branching hairs (Fig. 266), which entangle
Fig. 267. — Adaptive modifications of the legs of the worker honey bee. A, outer
aspect of left hind leg; B, portion of left middle leg; C, inner aspect of tibio-tarsal region of
left hind leg; D, tibio-tarsal region of left fore leg; a, antenna comb; au, auricle; b, brush;
c, coxa; co, corbiculum;/, femur; p, pecten; pc, pollen combs; s, spur; sp, spines; ss, spines; t,
trochanter; ii, tibia; v, velum; w, so-called wax pincers; 1-5, tarsal segments; i, metatarsus,
or planta.
pollen grains. These are combed out of the gathering hairs by means
of special pollen combs (Fig. 267, C, pc) on the inner surface of the
planta of the hind tarsus, the middle legs also assisting in this operation.
From these combs, the pollen is transferred to the pollen baskets, or
corbicula (Fig. 267, A, co), of the outer surface of each hind tibia, the
pollen from one side being transferred to the corbiculum of the opposite
side. This is accomplished in the following, manner: the left pecten
combs out the pollen from the right planta and a mass of pollen forms
just above the left pecten at the lower end of the corbiculum; this mass
. gradually grows larger and is pushed up along the corbiculum by the
INSECTS IN RELATION TO PLANTS 229
upward movement of the auricle: Further details are given by Casteel,
whose admirably precise and thorough studies on the manipulation of
pollen and wax by the honey bee have corrected certain prevalent
errors and added much to our knowledge of the subject. Arriving at
the nest, the hind legs are thrust into a cell and the mass of pollen on
each corbiculum is pried out by means of a spur situated at the apex
of the middle tibia (Fig. 267, B, s), this lever being slipped in at the
upper end of the corbiculum and then pushed along the tibia under the
mass of pollen; the spur is used also in cleaning the wings, which ex-
plains its presence on queen and drone, as well as worker, but the pollen-
gathering structures of the hind legs are confined to the worker.
The so-called wax-pincers of the hind legs (Fig. 267, A, C, w) at the
tibio-tarsal articulation, have nothing to do with the transfer of wax
scales from the abdomen to the mouth, according to Casteel; a wax scale
being removed from its pocket by becoming impaled on stiff spines
at the distal end of the inner face of the planta.
For cleaning the antennae, a front leg is passed over an antenna,
which slips into a semicircular scraper (Fig. 267, D, a) fashioned from
the basal segment of the tarsus; when the leg is bent at the tibio-tarsal
articulation, an appendage, or velum {v) of the tibia falls into place to
complete a circular comb, through which the antenna is drawn. This
comb is itself cleaned by means of a brush of hairs (6) on the front margin
of the tibia. A series of erect spines (sp) along the anterior edge of the
first tarsal segment is used as an eye brush, to remove pollen grains or
other foreign bodies from the hairs of the compound eyes. The labium
and maxillae (Fig. 56) are exquisitely constructed with reference to
gathering and sucking nectar; the maxillae are used also to smooth the
cell walls of the comb; the mandibles (Fig. 56, md), notched in queen
and drone but with a sharp entire edge in the worker, are used for cut-
ting, scraping and moulding wax, as well as for other purposes. The
entire digestive system of the honey bee is adapted in relation to nectar
and pollen as food; the proventriculus forms a reservoir for honey and
is even provided at its mouth with a rather complex apparatus for strain-
ing the honey from the accompanying pollen grains, as described by
Cheshire. The wax glands (Fig. 104) are remarkable speciahzations in
correlation with the food habits, as are also the various cephaHc glands,
the chief functions of which are given as: (i) digestion, as the conversion
of cane sugar into grape sugar, and possibly starch into sugar; (2) the
chemical alteration of wax; (3) the production of special food substances,
which are highly important in larval development.
230
ENTOMOLOGY
Numerous special sensory adaptations also occur. In fact, the
whole organization of the honey bee has become profoundly modified
in relation to nectar and pollen. Many other insects have the same
food but none of them sustain such intimate relations to the flowers as
do the bees.
Ant-plants. — There are several kinds of tropical plants which are
admirably suited to the ants that inhabit them. Indeed, it is often as-
serted that these plants have become modified with special reference to
their use by ants, though this is a gratuitous and improbable assumption.
Belt found several species of Acacia in Nicaragua and the Amazon
valley which have large hollow stipular thorns, inhabited by ants of the
genus Pseudomyrma. The ants enter by boring a hole near the apex of
Fig. 268. — Acacia sphcerocephala, an ant-plant, b, one of the " Belt's bodies"; g, gland;
s, s, hollow stipular thorns, perforated by ants. Reduced. — From Strasburger's Lehrbiich
der Botanik.
a thorn (Fig. 268, s). The plant affords the ants food as well as shelter,
for glands ig) at the bases of the petioles secrete a sugary fluid, while
many of the leaflets are tipped with small egg-shaped or pear-shaped
appendages {h) known as "Belt's bodies," which are rich in albumin,
fall off easily at a touch, and are eaten by the ants. These ants drive
away the leaf-cutting species, incidentally protecting the tree in which
they live.
The ant- trees {Cecropia adenopus) of Brazil and Central America
have often been referred to by travelers. When one of these trees is
handled roughly, hosts of ants rush out from small openings in the stems
and pugnaciously attack the disturber. Just above the insertion of
each leaf is a small pit (Fig. 269, a, b) where the wall is so thin as to form
a mere diaphragm, through which an ant (probably a fertilized female)
bores and reaches a hollow internode. To establish communication be-
tween the internodal chambers, the ants bore through the intervening
INSECTS IN RELATION TO PLANTS
23]
septa (Fig. 270). They seldom leave the Cecropia plant, unless dis-
turbed, and even keep herds of aphids in their abode. The base of each
petiole bears (Fig. 271) tender little egg-like bodies ("Miiller's bodies")
which the ants detach, store away and eat ; the presence of these bodies
is a sure sign that the tree is uninhabited by these ants, which, by the
way, belong to the genus Azteca.
It is too much to assert that the ants protect the Cecropia plant in
return for the food and shelter which they obtain. All ants are hostile
Fig. 269. — Portion of young stem of Cecropia aden-
opus showing internodal pits, o and b. Natural size.
Figures 269-271 are from Schimper's Pflanzengeo-
graphie.
Fig. 270. — Cecropia adenopus.
Portion of a stem, split so as to
show internodal chambers and the
intervening septa perforated by
ants.
to all other species of ants, with few exceptions, and even to other col-
onies of their own species; so that their assaults upon leaf-cutting ants
are by no means special and adaptive in their nature, and any protec-
tion that a plant derives therefrom is merely incidental. Furthermore,
hollow stems, glandular petioles and pitted stems are of common
occurrence when they bear no relation to the needs of ants. These
interrelations of ants and plants are too often misinterpreted in
popular and uncritical accounts of the subject.
The interesting habits of the leaf-cutting ants in relation to the
ENTOMOLOGY
plants that they attack are described in a subsequent chapter, where
will be found also an account of the Harvesting ants.
The epiphytic plants Myrmecodia and Hydnophytum, of Java, form
/
Fig. 271. — Cecropiaadenopus. Base of Fig. 272. — Hydnophytum monlannm. Sec-
petiole showing "Muller's bodies." tionof pseudo-bulb, to show chambers inhabited
Slightly reduced. by ants. One-fourth natural size. — A f t e r
FOREL.
spongy bulb-like masses, the chambers of which are usually tenanted by
ants, which rush forth when disturbed. These lumps (Fig. 272) are
primarily water-reservoirs, but the ants utilize them by boring into them
and from one chamber into another. In plants of the genus Humholdtia
the ants can enter the hollow internodes through openings that already
exist.
CHAPTER VIII
INSECTS IN RELATION TO OTHER AXIM.VLS
On the one hand, insects may derive their food from other animals,
either living or dead; on the other hand, insects themselves are food for
other animals, especially fishes and birds, against which they protect
themselves by various means, more or less effective. These topics form
the principal subject of the present chapter.
Predaceous Insects. — Innumerable aquatic insects feed largely or
entirely upon microscopic Protozoa, Rotifera, Entomostraca, etc.; this
is especially the case with culicid (mosquito) and chironomid( midge)
larvae. Many aquatic Hemiptera and Coleoptera prey upon planarians,
nematodes, annelids, molluscs and crustaceans; Belostoma (the electric
light bug) sometimes pierces the bodies of tadpoles and small fishes;
Dytiscus also kills young fishes occasionally and is distinctly carnivorous
both as larva and imago. Among terrestrial insects, the ground beetles,
Carabidae, are notably predaceous, preying not only upon other insects
but also upon molluscs, myriopods, mites and spiders. Ants do not
hesitate to attack all kinds of animals; in the tropics the wandering
ants (Eciton) attack lizards, rats and other vertebrates, and it is said
that even huge serpents, when in a torpid condition, are sometimes
killed by armies of these pugnacious insects.
Mosquitoes affect not only mammals but also, though rarely, fishes
and turtles. The gadflies (Tabanidae) torment horses and cattle by
their punctures; and the black-flies, or buffalo gnats {Simulium), per-
secute horses, mules, cattle, fowls, and frequently become unendurable
even to man. The notorious tsetse fly {Glossina morsitans) of South
Africa spreads a deadly disease among horses, cattle and dogs, by inocu-
lating them with a protozoan blood-parasite, to the effects of which,
.fortunately, man is not susceptible.
Parasitic Insects. — Insects belonging to several diverse orders have
become peculiarly modified to exist as parasites either upon or within
the bodies of birds or mammals.
Almost all birds are infested by Mallophaga, or bird lice, of which
Kellogg has catalogued 264 species from 257 species of North American
birds. Sometimes a species of Mallophaga is restricted to a single
234 ENTOMOLOGY
species of bird, though in the majority of cases this is not so. Several
mallophagan species often infest a single bird; thus nine species occur
on the hen, and no less than twelve" species, representing five genera, on
the American coot. These parasites spread by contact from male to
female, from old to young, and from one bird to another when the birds
are gregarious. When a single species of bird louse occurs on two or
more hosts, these are almost always closely allied, and Kellogg has sug-
gested the interesting possibility that such a species has persisted un-
changed from a host which was the common ancestor of the two or more
present hosts. Mallophaga are not altogether limited to birds, how-
ever, for they may be found on cattle, horses, cats, dogs, and some other
mammals; Kellogg records eighteen species from fifteen species of mam-
mals. These biting lice feed, not upon blood, but upon epidermal
cells and portions of feathers or hairs. They have fiat tough bodies
(Fig. i8), with no traces of wings, and a large head with only simple eyes;
the eggs are glued to feathers or hairs.
Mammals only are infested by the sucking lice, or Pediculidae.
These (Fig. 24) have a large oval or rounded abdomen, no wings, a
small head, minute simple eyes or none, and claws that are adapted to
clutch hairs; the eggs are glued to hairs. Sucking Hce affect horses,
cattle, sheep, dogs, monkeys, seals, elephants, etc., and man is para-
sitized by three species, namely, the head louse (Pediculus humanus
capitis), the body louse {Pediculus humanus corporis), and the crab
louse {Phthirius pubis) .
An anomalous beetle, Platypsyllus castoris, occurs throughout North
America and also in Europe as a parasite of the beaver.
The iieas, allied to Diptera but constituting a distinct order (Siphon-
aptera), are familiar parasites of chickens, cats, dogs and human beings.
These insects (Fig. 32) are well adapted by their laterally compressed
bodies for slipping about among hairs, and their saltatory powers and
general elusiveness are well known. Their wings are reduced to mere
rudiments, their eyes when present are minute and simple and their
mouth parts are suctorial.
Among Diptera, there are a few external parasites, the best known
of which is the sheep tick {Melophagus ovinus), though several highly
interesting but little-studied forms are parasitic upon birds and bats.
The larvae of the bot-flies (CEstridae) are common internal parasites
of mammals. The sheep bot-fly {CEstrus avis) deposits her eggs or
larvae on the nostrils of sheep; the maggots develop in the frontal sinuses
of the host, causing vertigo or even death, and when full grown escape
INSECTS IN RELATION TO OTHER ANIMALS 235
through the nostrils and pupate in the soil. The horse bot-fly {Gastro-
philus equi) glues its eggs to the hairs of horses, especially on the fore
legs and shoulders, whence the larvae are licked off and swallowed; once
in the stomach, the bots fasten themselves to its lining, by means of
special hooks, and withstand almost all efforts to dislodge them ; though
when the bots have attained their growth they release their hold and
pass with the excrement to the soil. Bots of the genus Hypoderma form
tumors on cattle and other mammals, domesticated or wild. The ox-
warble (//. lineata, Fig. 213, /) reaches the oesophagus of its host in the
same manner as the horse bot, according to Curtice, but then makes
its way into the subcutaneous tissue and causes the well-known tumors
on the back of the animal; when full grown the bots squirm out of these
tumors and drop to the ground, leaving permanent holes in the hide.
Parasitism in General. — Parasitic insects evidently do not consti-
tute a phylogenetic unit, but the parasitic habit has arisen independently
in many different orders. These insects do, however, agree superficially,
in certain respects, as the result of what may be termed convergence of
adaptation. Thus a dipterous larva, living as an internal parasite, in
the presence of an abundant supply of food, has no legs, no eyes or anten-
nae, and the head is reduced to a mere rudiment, sufficient simply to
support a pair of feeble jaws; the skin, moreover, is no longer armor-like
but is thin and delicate, the body is compact and fleshy, and the diges-
tive system is of a simplified type. The same modifications are found in
hymenopterous larvae, under similar food-conditions, except that the
head undergoes less reduction. The various external parasites lack
wings, almost invariably, and the eyes, instead of being compound,
are either simple or else absent. In some special cases, as in a few
dipterous parasites of birds and bats, the wings are present, either
permanently or only temporarily, enabhng the insects to reach their
hosts.
This so-called parasitic degeneration, widespread among animals in
general and consisting chiefly in the reduction or loss of locomotor and
sensory functions in correlation with an immediate and plentiful supply
of food, results in a simplicity of organization which is to be regarded —
not as a primitive condition — but as an expression of what is, in one
sense, a high degree of specialization to peculiar conditions of life.
This exquisite degree of adaptation to a special environment, however,
sacrifices the general adaptability of the animal, — makes it impossible
for a parasite to adapt itself to new conditions; and while parasitism
may be an immediate advantage to a species, there are few parasites
236 ENTOMOLOGY
that have attained any degree of dominance among animals. Ichneu-
monidas, to be sure, are remarkably dominant among insects, but their
parasitic adaptations are limited for the most part to the larval stage,
and the adults may be said to be as free for new adaptations as are any
other Hymenoptera.
Scavenger and Carrion Insects. — Not a few families of Diptera
and Coleoptera derive their food from dead animal matter. The
aquatic families Dytiscidae and Gyrinidae are largely scavengers.
Among terrestrial forms, Silphidae feed on dead animals of all kinds;
the burying beetles (Necrophorus), working in pairs, undermine and
bury the bodies of birds, frogs and other small animals, and lay their
eggs in the carcasses; Histeridae and Staphylinidae are carrion beetles,
and Dermestidae attack dried animal matter of almost every description,
their depredations upon furs, feathers, museum specimens, etc., being
famihar to all. Ants are famous as scavengers, destroying decaying
organic matter in immense quantities, particularly in the tropics.
Many Scarabaeidae feed upon excrementitious matter, for example the
"tumble-bugs," which are frequently seen in pairs, laboriously rolUng
along or burying a large ball of dung, which is to serve as food for the
larva.
Insects as Food for Vertebrates.— Lizards, frogs, and toads are
insectivorous, especially toads. The American toad feeds chiefly upon
insects, which form 77 per cent, of its food for the season, the remainder
consisting of myriopods, spiders, Crustacea, molluscs and worms, accord-
ing to the observations of A. H. Kirkland, who states that Lepidoptera
form 28 per cent, of the total insect food, Coleoptera 27, Hymenoptera
19 and Orthoptera 3 per cent. The toad does not capture dead or
motionless insects but uses its extensile sticky tongue to Kck in moving
insects or other prey, which it captures with surprising speed and preci-
sion. In the cities one often sees many toads under an arc-light engaged
in catching insects that fall anywhere near them. Though its diet is
varied and somewhat indiscriminate, the toad consumes such a large
proportion of noxious insects, such as May beetles and cutworms, that
it is unquestionably of service to man.
Moles are entirely insectivorous and destroy large numbers of white
grubs and caterpillars; field mice and prairie squirrels eat many insects,
especially grasshoppers, and the skunk revels in these insects, though it
eats beetles frequently, as does also the raccoon, which is to some extent
insectivorous. Monkeys are omnivorous but devour many kinds of
insects.
INSECTS IN RELATION TO OTHER ANIMALS 237
With these hasty references, we may pass at once to the subject of
the insect food of fishes and birds.
Insects in Relation to Fishes. — Insects constitute the most impor-
tant portion of the food of adult fresh water fishes, furnishing forty
per cent, of their food, according to Dr. Forbes, from whose valuable
writings the following extracts are taken.
"The principal insectivorous fishes are the smaller species, whose
size and food structures, when adult, unfit them for the capture of Ento-
mostraca, and yet do not bring them within reach of fishes or Mollusca.
Some of these fishes have peculiar habits which render them especially
dependent upon insect Hfe, the Httle minnow Phenacohius, for example,
which, according to my studies, makes nearly all its food from insects
(ninety-eight per cent.) found under stones in running water. Next are
the pirate perch, Aphredoderus (ninety-one per cent.), then the darters
(eighty-seven per cent.), the croppies (seventy-three per cent.), half-
grown sheepshead (seventy-one p&c cent.), the shovel fish (fifty-nine per
cent.), the chub minnow (fifty-six per cent.), the black warrior sunfish
{ChcBnohryttus) and the brook silversides (each fifty-four per cent.) , and
the rock bass and the cyprinoid genus Notropis (each fifty-two per
cent.).
"Those which take few insects or none are mostly the mud-feeders
and the ichthyophagous species, Amia (the dog-fish) being the only
exception noted to this general statement. Thus we find insects wholly
or nearly absent from the adult dietary of the burbot, the pike, the gar,
the black bass, the wall-eyed pike, and the great river catfish, and from
that of the hickory shad and the mud-eating minnows (the shiner, the
fathead, etc.). It is to be noted, however, that the larger fishes all go
through an insectivorous stage, whether their food when adult be almost
wholly other fishes, as with the gar and the pike, or molluscs, as with the
sheepshead. The mud-feeders, however, seem not to pass through this
stage, but to adopt the limophagous habit as soon as they cease to
depend upon Entomostraca.
"Terrestrial insects, dropping into the water accidentally or swept
in by rains, are evidently diHgently sought and largely depended upon
by several species, such as the pirate perch, the brook minnow, the top
minnows or kilHfishes (cyprinodonts) the toothed herring and several
cyprinoids {Semotilus, Pimephales and Notropis).
"Among aquatic insects, minute slender dipterous larvse, belonging
mostly to Chironomus, Corethra and allied genera are of remarkable
importance, making, in fact, nearly one tenth of the food of all the fishes
238 ENTOMOLOGY
studied. They are most abundant in Phenacohius and Etheostoma,
which genera have become especially adapted to the search for these
insect forms in shallow rocky streams. Next I found them most gener-
ally in the pirate perch, the brook silversides, and the stickleback, in
which they averaged forty-five per cent. They amounted to about one
third the food of fishes as large and important as the red horse and the
river carp, and made nearly one fourth that of fifty-one buffalo fishes.
They appear further in considerable quantity in the food of a number of
the minnow family {Notropis, Fimephales, etc.), which habitually fre-
quent the swift waters of stony streams, but were curiously deficient in
the small collection of miller's thumbs (Cottidae) which hunt for food in
similar situations. The sunfishes eat but few of this important group,
the average of the family being only six per cent.
''Larvae of aquatic beetles, notwithstanding the abundance of some
of the forms, occurred in only insignificant ratios, but were taken by
fifty-six specimens, belonging to nineteen of the species,— more fre-
quently by the sunfishes than by any other group. The kinds most
commonly captured were larvae of Gyrinidae and Hydrophilidae ; where-
as the adult surface beetles themselves {Gyrinus, Dineutes, etc.) — whose
zigzag-darting swarms no one can have failed to notice — were not once
encountered in my studies.
"The almost equally well-known slender water-skippers [Gerris] seem
also completely protected by their habits and activity from capture
by fishes, only a single specimen occurring in the food of all my specimens.
Indeed, the true water bugs (Hemiptera) were generally rare, with the
exception of the small soft-bodied genus Corixa which was taken by
one hundred and ten specimens, belonging to twenty-seven species,
— most abundantly by the sunfishes and top minnows.
"From the order Neuroptera [in the broad sense] fishes draw a
larger part of their food than from any other single group. In fact,
nearly a fifth of the entire amount of food consumed by all. the adult
fishes examined by me consisted of aquatic larvae of this order, the great-
er part of them larvae of day flies (Ephemeridae), principally of the genus
Hexagenia. These neuropterous larvae were eaten especially by the
miller's thumb, the sheepshead, the white and striped bass, the common
perch, thirteen species of the darters, both the black bass, seven of the
sunfishes, the rock bass and the croppies, the pirate perch, the brook
silversides, the sticklebacks, the mud minnow, the top minnows, the
gizzard shad, the toothed herring, twelve species each of the true
minnow family and of the suckers and buffalo, five catfishes, the dog-
INSECTS IN RELATION TO OTHER ANIMALS 239
fish, and the shovel fish, — seventy species out of the eighty-seven which
I have studied.
"Among the above, I found them the most important food of the
white bass, the toothed herring, the shovel fish (fifty-one per cent.), and
the croppies; while they made a fourth or more of the alimentary con-
tents of the sheepshead (forty-six per cent.), the darters, the pirate
perch, the common sunfishes (Lepomis and Chanohryltus) , the rock
bass, the little pickerel, and the common sucker (thirty-six per
cent.).
"Ephemerid larvae were eaten by two hundred and thirteen speci-
mens of forty-eight species— not counting young. The larva of Hexa-
genia, one of the commonest of the 'river flies,' was by far the most
important insect of this group, this alone amounting to about half of
all the Neuroptera eaten. It made nearly one half of the food of the
shovel fish, more than one tenth that of the sunfishes, and the princi-
pal food resource of half-grown sheepshead; but was rarely taken by
the sucker family, and made only five per cent, of the food of the catfish
group.
"The various larvae of the dragon flies, on the other hand, were much
less frequently encountered. They seemed to be most abundant in
the food of the grass pickerel (twenty-five per cent.) and next to that,
in the croppie, the pirate perch, and the common perch (ten to thirteen
percent.).
"Case-worms (Phryganeidae) were somewhat rarely found, rising to
fifteen per cent, in the rock bass and twelve per cent, in the minnows of
the Hybopsis group, but otherwise averaging from one to six per cent,
in less than half of the species."
Insects in Relation to Birds. — From an economic point of view the
relations between birds and insects are extremely important, and from
a purely scientific standpoint they are no less important, involving as
they do biological interactions of remarkable complexity.
The prevalent popular opinion that birds in general are of inesti-
mable value as destroyers of noxious insects is a correct one, as Dr.
Forbes proved, from his precise and extensive studies upon the food of
Ilhnois birds, involving a laborious and difficult examination of the
stomach contents of many hundred specimens. All that follows is
taken from Forbes, when no other author's name is mentioned, and
though the percentages given by him apply to particular years and would
undoubtedly vary more or less from year to year, they are here for con-
venience regarded as representative of any year and are spoken of in
240 ENTOMOLOGY
the present tense. About two thirds of the food of birds consists of
insects.
Robin. — The food of the robin in Ilhnois, from February to May in-
clusive, consists almost entirely of insects; at first, larvae of Bibio albi-
pennis for the most part, and then caterpillars and various beetles. When
the small fruits appear, these are largely eaten instead of insects; thus
in June, cherries and raspberries form fifty-five per cent, and insects
(ants, caterpillars, wireworms and Carabidae) forty-two per cent, of the
food; and in July, raspberries, blackberries and currants form seventy-
nine per cent, and insects (mostly caterpillars, beetles and crickets) but
twenty per cent, of the food. In August, insects rise to forty-three per
cent, and fruits drop to fifty-six per cent., and these are mostly cherries,
of which two thirds are wild kinds. In September, ants form fifteen
per cent, of the food, caterpillars five per cent, and fruits (mostly grapes,
mountain-ash berries and moonseed berries) seventy per cent. In
October, the food consists chiefly of wild grapes (fifty- three per cent.),
ants (thirty-five per cent.), and caterpillars (six per cent.).
For the year, judging from the stomach contents of one hundred and
fourteen birds, garden fruits form only twenty-nine per cent, of the food
of the robin, while insects constitute two thirds of the food. The results
are confirmed by those of Professor Beal in Michigan, who found that
more than forty-two per cent, of the food of the robin consists of insects
with some other animal matter, the remainder being made up of various
small fruits, but notably the wild kinds.
Upon the whole, the robin deserves to be protected as an energetic
destroyer of cutworms, white grubs and other injurious insects, and the
comparatively few cultivated berries that the bird appropriates are
ordinarily but a meagre compensation for the valuable services rendered
to man by this familiar bird.
Catbird. — Not so much can be said for the catbird, however, for,
though its food habits are similar to those of the robin, it arrives later
and departs earher, with the result that it is less dependent than the
robin upon insects and that berries form a larger percentage of its
total food.
In May, eighty-three per cent, of the food of the catbird consists of
insects, mostly beetles (Carabidae, Rhynchophora, etc.), crane-flies,
ants and caterpillars (Noctuidae) ; while dry sumach berries are eaten to
the extent of seven per cent. For the first half of June, the record is
much the same, with an increase, however, in the number of May
INSECTS IN RELATION TO OTHER ANIMALS 24I
beetles eaten; in the second half of the month the food consists chiefly
of small fruits, especially raspberries, cherries and currants; so that for
the month as a whole, only forty-nine per cent, of the food is made up
of insects. This falls to eighteen per cent, in July, when three quarters
6f the food consists of small fruits, mostly blackberries, however. In
August, with the diminution of the smaller cultivated fruits, the per-
centage of insects rises to forty-six per cent., nearly one half of which is
made up of ants and the rest of caterpillars, grasshoppers, Hemiptera,
Coleoptera, etc. In September, with the appearance of wild cherries,
elderberries, Virginia creeper berries and grapes, these are eaten to the
extent of seventy-six per cent., the insect element of the food falling to
twenty-one per cent., of which almost half consists of ants, and the
remainder of beetles and a few caterpillars.
For the entire year, as appears from the study of seventy specimens
by Forbes, insects form forty-three per cent, of the food of the catbird
and fruits fifty-two per cent. As the injurious insects killed are offset
by the beneficial ones destroyed, "the injury done in the fruit-garden by
these birds remains without compensation unless we shall find it in the
food of the young," says Professor Forbes. And this has been found, to
the credit of the catbird; for Weed learned that the food of three nest-
lings consisted of insects, sixty-two per cent, of which were cutworms
and four per cent, grasshoppers; while Judd found that fourteen nest-
lings had eaten but four per cent, of fruit, the diet being chiefly ants,
beetles, caterpillars, spiders and grasshoppers. In fact, Weed believes
that, on the whole, the benefit received from the catbird is much greater
than the harm done, and that its destruction should never be permitted
except when necessary in order to save precious crops.
Bluebird. — The excellent reputation which the bluebird bears every-
where as an enemy of noxious insects is well deserved. From a study of
one hundred and eight Illinois specimens, Forbes finds that seventy-
eight per cent, of the food for the year consists of insects, eight per cent,
of Arachnida, one per cent, of Julidse and only thirteen per cent, of
vegetable matter, edible fruits forming merely one per cent, of the entire
food. The insects eaten are mostly caterpillars (chiefly cutworms),
Orthoptera (grasshoppers and crickets) and Coleoptera (Carabidae and
Scarabaeidae) . Though some of the insects are more or less beneficial to
man, such as Carabidae and Ichneumonidae (respectively predaceous and
parasitic), the beneficial elements form only twenty-two per cent, of the
food for the year, as against forty-nine percent, of injurious elements, the
remaining twenty- nine per cent, consisting of neutral elements. The food
242 » ENTOMOLOGY
of the nestlings, according to Judd, is essentially like that of the adults,
being "beetles, caterpillars, grasshoppers, spiders and a few snails."
Other Insectivorous Birds. — Weed and Dearborn, from whose
excellent work the following notes are taken, find that the common
chickadee devours immense numbers of canker worms, and that more
than half its food during winter consists of insects, largely in the form of
eggs, including those of the common tent caterpillar (C. americana),
the fall webworm {H. cunea) and particularly plant lice, whose eggs,
small as they are, form more than one fifth of the entire food ; more than
four hundred and fifty of them are sometimes eaten by a single bird in
one day, and the total number destroyed annually is inconceivably
large. The house wren is almost exclusively insectivorous, feeding
upon caterpillars and other larvae, ants, grasshoppers, gnats, beetles,
bugs, spiders, and myriopods. The swallows, also, are highly insecti-
vorous; ''most of their food is captured on the wing, and consists of
small moths, two-winged flies, especially crane flies, beetles in great
variety, flying bugs, and occasionally small dragon flies. The young
are fed with insects." Ninety per cent, of the food of the kingbird
"consists of insects, including such noxious species as May beetles,
click-beetles, wheat and fruit weevils, grasshoppers, and leafhoppers."
The honey bees eaten by this bird are insignificant in number. Wood-
peckers destroy immense numbers of wood-boring larvae, bark-insects,
ants, caterpillars, etc. The cuckoos "are unique in having a taste for
insects that other birds reject. Most birds are ready to devour a smooth
caterpillar that comes their way, but they leave the hairy varieties
severely alone. The cuckoos, however, make a specialty of devouring
such unpalatable creatures; even stink bugs and the poisonous spiny
larvae of the lo moth are freely taken." Caterpillars form fifty per
cent, of the food for the year; Orthoptera (grasshoppers, katydids, and
tree crickets), thirty per cent.; Coleoptera and Hemiptera, six per cent,
each; and flies and ants are taken in small quantities. "The nestling
birds are fed chiefly with smooth caterpillars and grasshoppers, their
stomachs probably being unable to endure the hairy caterpillars. All
in all, the cuckoos are of the highest economic value. They do no
harm and accomplish great good. If the orchardist could colonize
his orchards with them, he would escape much loss." The quail feeds
largely upon insects during the summer, frequently eating the Colorado
potato beetle and the army worm; the prairie hen has similar food
habits but lives almost exclusively on grasshoppers, when these are
abundant.
INSECTS IN RELATION TO OTHER ANIMALS 243
The Insect Food of Birds. — ''There are few groups of injurious
insects that enter so largely into the composition of the food of birds as
do the locusts, or short-horned grasshoppers, of the family Acridiidce
[now Locustidajj. The enormous destructive power of these insects
is well known, but our indebtedness to birds in checking their oscilla-
tions is less generally recognized." Professor Aughey, who has made
extensive studies upon the relation of birds to the Rocky Mountain
locust, found that upon one occasion 6 robins had eaten 265 of these
insects, 5 catbirds 152, 3 blue-birds 67, 7 barn swallows 139, 7 night
hawks 348, 16 yellow-billed cuckoos 416, 8 flickers 252, 8 screech owls
219, and I humming bird 4; while crows and blue-jays had eaten large
numbers of the locusts; and grouse, quail and prairie hen, enormous num-
bers. Even shore birds, such as geese, ducks, gulls and pelicans came to
share in the feast. Aughey estimated that the locusts eaten in one day
by the passerine birds of the eastern half of Nebraska were sufficient to
destroy in a single day 174,397 tons of crops, valued at $1,743.97.
Weed and Dearborn state that, of Hemiptera, Jassidae are very often
found in the stomachs of birds, and that aphids and their eggs form a
large part of the food of many of the smaller birds, such as the warblers,
nuthatches, kinglets and chickadees. A large proportion of the cater-
pillars of the Lepidoptera are eagerly devoured by birds, forming an
important element of the food of many species. The hairy caterpillars
are eaten by cuckoos and blue-jays and the large saturniid caterpillars,
such as cecropia and polyphemus, by some of the hawks. Almost all
kinds of Goleoptera are food for birds, but especially the grubs of Scara-
baeidae, which are eagerly devoured by robins, blackbirds, crows and
other birds. Of the Diptera, Itonididae and other gnats are eaten
by swallows, swifts and night hawks; while crane flies, TipuHdae, are
often found in the stomachs of birds. Among Hymenoptera, ants are
eaten extensively by woodpeckers, catbirds and many other species, as
are also Ichneumonidae and other parasitic forms — these last by the
flycatchers in particular.
The Regulative Action of Birds upon Insect Oscillations.^ The worst
injuries by insects are done by species that fluctuate excessively in
number as the result of variations in those manifold forces that act as
checks upon the multiplication of the species.
In order to determine whether birds do anything to reduce existing
oscillations of injurious insects, Professor Forbes made studies upon the
food of birds which were shot in an IlHnois apple orchard which was
being ravaged by canker-worms. In this orchard, birds were present in
244 ENTOMOLOGY
extraordinary number and variety, there being at least thirty-five
species-, most of which were studied by Forbes, from whose exhaustive
tables the following food-percentages are taken:
Birds Insects, Canker-worms,
Examined Per Cent. Per Cent.
Robin 9 93 21
Catbird 14 98 ^5
Brown Thrush 4 94 12
Bluebird 5 9S 12
Black-capped Chickadee 2 100 61
House Wren 5 91 46
Tennessee Warbler i 100 80
Summer Yellow Bird 5 94 67
Black- throated Green Warbler i 100 7° .
Maryland Yellow-throat 2 100 37
Baltimore Oriole 3 1°° 40
To quote Forbes: "Three facts stand out very clearly as results of
these investigations: i. Birds of the most varied character and habits,
migrant and resident, of all sizes, from, the tiny wren to the blue-jay,
birds of the forest, garden and meadow, those of arboreal and those of
terrestrial habits, were certainly either attracted or detained here by the
bountiful supply of insect food, and were feeding freely upon the species
most abundant. That thirty-five per cent, of the food of all the birds
congregated in this orchard should have consisted of a single species of
insect, is a fact so extraordinary that its meaning can not be mistaken.
Whatever power the birds of this vicinity possessed as checks upon
destructive irruptions of insect life was being largely exerted here to
restore the broken balance of organic nature. And while looking for
their influence over one insect outbreak we stumbled upon at least two
others, less marked, perhaps incipient, but evident enough to express
themselves clearly in the changed food ratios of the birds.
"2. The comparisons made show plainly that the reflex efi'ect of this
concentration on two or three unusually numerous insects was so widely
distributed over the ordinary elements of their food that no especial
chance was given fcir the rise of new fluctuations among the species
commonly eaten. That is to say, the abnormal pressure put upon the
cankerworm and vine-chafer was compensated by a general diminution
of the ratios of all the other elements, and not by a neglect of one or two
alone. If the latter had been the case, the criticism might easily have
been made that the birds, in helping to reduce one oscillation, were
setting others on foot.
"3. The fact that, with the exception of the indigo bird, the species
INSECTS IN RELATION TO OTHER ANIMALS 245
whose records in the orchard were compared with those made elsewhere
had eaten in the former situation as many caterpillars other than canker-
worms as usual, simply adding their canker-worm ratios to those of other
caterpillars, goes to show that these insects are favorites with a majority
of birds."
The Relations of Birds to Predaceous and Parasitic Insects. — The
false assumption is often made that a bird is necessarily inimical to
man's interest whenever it destroys a parasitic or a predaceous insect.
Weed and Dearborn attack this assumption as follows:
"Suppose an ichneumon parasite is found in the stomach of a robin
or other bird: it may belong to any one of the following categories:
"i. The primary parasite of an injurious insect.
"2. The secondary parasite of an injurious insect.
"3. The primary parasite of an insect feeding on a noxious plant.
"4. The secondary parasite of an insect feeding on a noxious plant.
"5. The primary parasite of an insect feeding on a wild plant of no
economic value.
"6. The secondary parasite of an insect feeding on a wild plant of no
economic value.
"j. The primary parasite of a predaceous insect.
"8. The primary parasite of a spider or a spider's egg.
"This hst might easily be extended still farther, and the assumption
that the parasite belongs to the first of these categories is unwarranted
by the facts and does violence to the probabilities of the case.
"A correct idea of the economic role of the feathered tribes may be
obtained only by a broader view of nature's methods, — a view in which
we must ever keep before the mind's eye the fact that all the parts of
the organic world, from monad to man, are linked together in a thousand
ways, the net result being that unstable equilibrium commonly called
'the balance of nature.'"
The general subject of food relations and interactions of insects is
taken up in the chapter on ecology (page 373).
Efficiency of Protective Adaptations of Insects. — Interesting from
a scientific point of view are the various adaptations by means of which
insects are protected more or less from their bird enemies. Colora-
tional adaptations having been discussed in another chapter, there
remain for consideration— (i) hairs, (2) stings, (3) odors, flavors and
irritants. Most of what follows is from an admirable paper by Dr. Judd,
whose data are based upon his examination of the stomach contents of
fifteen thousand birds.
246 ENTOMOLOGY
Hairs. — " Excepting two species of cuckoos, no species of bird in the
eastern United States, so far as I am aware, makes a business of feeding
upon hairy caterpillars." Judd observed that the fall web worm,
Hyphantria cunea, infesting a pear tree was not at all molested, in spite
of the fact that the tree was tenanted by three broods of birds at the
time, namely, kingbirds, orchard orioles and English sparrows. The
hairy arctiid caterpillars, however, are eaten by a few birds : the robin,
bluebird, catbird, sparrowhawk, cuckoos and shrikes; and the spiny
larvae of Vanessa antiopa by cuckoos and the Baltimore oriole; while
the hairy caterpillars of the gipsy moth are known to be eaten in Massa-
chusetts by no fewer than thirty-one species of birds, notably cuckoos,
Baltimore oriole, catbird, chickadee, blue- jay, chipping sparrow, robin,
vireos and the crow, these birds being of no little assistance in the sup-
pression of this pest. These are exceptional cases, however, and in
general the hairiness of caterpillars appears to be a highly effective
protection against most birds.
Stings. — Some birds (chewink, young ducks) are fatally affected by
eating honey bees. The blue-jays, however, will eat Bombus (bumble-
bees) and Xylocopa, and flycatchers and swallows feed habitually upon
stinging Hymenoptera, particularly Scoliidae, while a great many birds
eat Myrmicidae, or stinging ants. The formic acid of ants does not
protect them from wholesale destruction by birds; Judd found three
thousand ants in the stomach of a flicker. "Stingless ants pretend to
sting but many birds they do not deceive." The stinging caterpillar
of Automeris io is occasionally eaten by the yellow-billed cuckoo.
Aside from these exceptions, the stings of insects are an extremely
efficient means of defence.
Odors, Flavors and Irritants. — The malodorous Heteroptera in
general are food for most birds; Lygus, Reduviidae (assassin bugs) and
Pentatomidae (stink bugs) are eaten by song sparrows, and £w5c/?w/w5 by
blackbirds and crows. The odors of Heteroptera are by no means
universally protective.
Among Coleoptera, the showy, ill-scented or ill-flavored Coccinellidae
(lady beetles) are eaten by very few birds — the flycatchers and swallows
— and are refused by caged blue-jays and song sparrows even when
these birds are hungry. Of Chrysomehdae, the Colorado potato beetle
is refused by the catbird, blue-jay and song sparrow, and Diabrotica
is not often eaten, except by catbirds and thrushes. "The smaller
Carabidae (ground beetles) whether stinking or not, are eaten by
practically all land birds." Crows, blackbirds and jays eagerly swallow
INSECTS IN RELATION TO OTHER ANIMALS 247
the showy Calosoma scrutator, and the first two birds are especially fond
of Harpalus caliginosus and H. pennsylvanicus , and feedGalerita to their
young. "A score of smaller Carabidae (ground beetles) and Chryso-
melidae (leaf beetles) metallic and conspicuously colored, are habitually
eaten by birds that have an abundance of other insect food to pick from."
The stenches of Lampyrida? (firefly family) appear to be more effec-
tive than those of Carabidae. Telephorus is occasionally eaten, but Pho-
tinus rarely if at all. Chauliognathus is not eaten by many birds
(though flycatchers and swallows select this insect) and the genus is
regarded unfavorably by caged catbirds and blue-jays.
In regard to other insects, Judd finds that Epicauta (blister beetle)
with its irritant fluid, is immune from all but the kingbird; Cyllene
seldom occurs in the stomachs of birds; May flies and caddis flies,
however, are terribly persecuted, but swiftly flying Diptera and Odonata
are highly immune.
From such facts as these, Judd properly infers, "not cases of protec-
tion and nori^protection, but cases of greater and lesser efficiency of
protective devices."
CHAPTER IX
TRANSMISSION OF DISEASES BY INSECTS
It is commonly known that some kinds of insects are of vital impor-
tance to man as agents in the transmission of certain diseases. In
recent years immense progress has been made in our knowledge of insect-
borne diseases.
Malaria
So far as is known, malaria is transmissible only through the agency
of mosquitoes.
The malaria "germ," discovered in 1880 by the French army surgeon
Laveran, may be found as a pale, amoeboid organism {Laverania,
Fig. 273) in the red blood corpuscles of persons afflicted with the disease.
This organism {schizont, 2) grows at the expense of the haemoglobin of
the corpuscle (3-5) and its growth is accompanied by. an increasing
deposit of black granules (melanin), which are doubtless excretory in
their nature. At length, the amoebula divides into many spores (mero-
zoites, 6) which by the disintegration of the corpuscle are set free in the
plasma of the blood. Here many if not most of the spores, and the
pigment granules as well, are attacked and absorbed by leucocytes, or
white blood corpuscles, while some of the spores may invade healthy red
corpuscles and develop as before. The period of sporulation, as Golgi
found, is coincident with that of the "chill" experienced by the patient;
and quinine is most effective when administered just before the sporula-
tion period. The destruction of red blood corpuscles explains the pallid,
or ancemic, condition which is characteristic of malarial patients. In
three or four days the number of red corpuscles may be reduced from
5,000,000 per cubic millimeter — the normal number — to 3,000,000; and
in three or four weeks of intermittent fever, even to 1,000,000.
Authorities recognize at least three species of malaria parasites
affecting man: (i) the tertian (Plasmodium vivax), with an asexual cycle
of forty-eight hours, causing the fever to recur every two days; (2)
the quartan (P. malarice), with a cycle of sbventy-two hours, causing
fever every third day; and (3) the suhtertian or malignant form (Laver-
ania falciparum) of which there are three varieties (perhaps species) ,
with cycles of twenty-four or forty-eight hours, according to the variety.
248
Pig. 273. — Life history of malaria parasite, Lai'drawja/a/ci^arMTW. i, sporozoite, intro-
duced by mosquito into human blood; the sporozoite becomes a schizont. 2, young schi-
zont, which enters a red blood corpuscle. 3, young schizont in a red blood corpuscle. 4,
full-grown schizont, containing numerous granules of melanin. 5, nuclear division prei)ara-
tory to sporulation. 6, spores, or merozoites, derived from a single mother-cell. 7, young
macrogametocyte (female), derived from a merozoite and situated in a red blood corpuscle.
7a, young microgametocyte (male) derived from a merozoite. 8, full-grown macrogameto-
cyte. 8a, full-grown microgametocyte. In stages 8 and 8a the parasite is taken into the
stomach of a mosquito; or else remains in the human blood. 9, mature macrogamete,
capable of fertilization; the round black extruded object may probably be termed a "polar
body." 9a, mature microgametocyte, preparatory to forming microgametes. 96, resting
cell, bearing six flagellate microgametes (male). 10, fertilization of a macrogamete by a
motile microgamete. The macrogamete next becomes an ookinete. 11, ookinete, or
wandering cell, which penetrates into the wall of the stomach of the mosquito. 12,
ookinete in the outer region of the wall of the stomach, i.e., next to the body cavity. 13,
young oocyst, derived from the ookinete. 14, oocyst, containing sporoblasts, which are to
develop into sporozoites. 15, older oocyst. 16, mature oocyst, containing sporozoites,
which are liberated into the body cavity of the mosquito and carried along in the blood
of the insect. 17, transverse section of salivary gland of an Anopheles mosquito, showing
sporozoites of the malaria parasite in the gland cells surrounding the central canal.
1-6 illustrate schizogony (asexual production of spores); 7-16, sporogony (sexual pro-
duction of spores).
After Grassi and Leuckart, by permission of Dr. Carl Chun.
249
250 ENTOMOLOGY
Two or more sets of parasites in the human blood, sporulating at
different times, may cause the fever to recur at intervals that are
apparently irregular.
After several successive asexual generations, there are produced
merozoites which develop — no longer into schizonts — but into sexual
forms, or gavietes. These occur in red blood corpuscles either as
macrogametocytes (female, 7, 8) or as microgametocytes (male, 7a, 8a),
in which forms the parasite is introduced into the stomach of a mosquito
which has been feeding upon the blood of a malarial patient. The
macrogametocyte now leaves its blood corpuscle and becomes a spherical
macrogamete (9) ; and the microgametocyte also becomes spherical
{ga) ; but the latter puts forth a definite number {six, in L. falciparum,
gb) of flagella, or microgametes, which separate off as motile male bodies,
capable of fertihzing the macrogametes. A microgamete penetrates a
macrogamete (10) and the nucleus of the one unites with that of the
other. The fertilized macrogamete, or zygote, now becomes a migrating
cell, or ookinete (11), which penetrates almost through the wall of the
stomach of the mosquito (12) and then becomes a resting cell, or cyst.
This oocyst (13) grows rapidly and its contents develop, by direct nuclear
division, into sporohlasts (14, 15), which differentiate into spindle-
shaped sporozoites (16, 17). The sporozoites are liberated into the
body cavity of the mosquito, carried in the blood to the salivary glands
(as well as elsewhere) and thence along the hypopharynx into the
body of a human being, bird or other animal attacked by the
insect.
The role of the mosquito as the intermediary host of malarial organ-
isms was discovered by Manson and Ross and confirmed by Koch, Stern-
berg and others. It has been found repeatedly that certain mosquitoes
(Anopheles) after feeding on the blood of a malarial patient can transmit
the disease by means of their "bites" to healthy persons. Thus,
Anopheles mosquitoes were fed on the blood of malarial subjects in
Rome and then sent to London, where a son of Dr. Manson allowed him-
self to be bitten by the insects. Though previously free from the
malarial organism, he contracted a well-marked infection as the result
of the inoculation.
Furthermore, it is highly probable that malaria cannot be trans-
mitted to man except through the agency of the mosquito. This ap-
pears from the oft-cited experiment of Doctors Sambon and Low on the
Roman Campagna, a place notorious for malaria. There the experi-
menters lived during the malarial season of 1900, freely exposed to the
TRANSMISSION OF DISEASES BY INSECTS 25 1
emanations from the marsh and taking no precautions except to screen
their house carefully against mosquitoes and to retire indoors before
the insects appeared in the evening. Simply by excluding Anopheles
mosquitoes, with which the Campagna swarmed, these investigators
remained perfectly immune from the malaria which was ravaging the
vicinity.
In a later experiment on the island of Formosa, one company of
Japanese soldiers was protected from mosquitoes and suffered no
malaria, while a second and unprotected company contracted the
disease.
The evident preventive measures to be taken against malaria are
(i) the avoida;nce of mosquito bites, by means of screens, and washes of
eucalyptus oil, camphor, oil of pennyroyal, oil of tar, etc., appHed to
exposed parts of the body; (2) the isolation of malarial patients from
mosquitoes, in order to prevent infection; (3) the destruction of mosqui-
toes in their breeding places, especially by the use of kerosene and by
drainage. During unavoidable exposure in malarious regions, quinine
should be taken in doses of six to ten grains during the day at intervals
of four or five days (Sternberg) .
In Macedonia in 191 6 there were some 800,000 cases of malaria,
with 2,000 deaths in the French and AlHed army. Where the disease
was most severe Anopheles mosquitoes were present in enormous num-
bers. A striking peculiarity of this epidemic was the marked failure
of quinine as a preventive or remedy. This failure was explained as
being due to the development of quinine-resistant strains of the malaria
parasites.
Culex and Anopheles.^ — More than five hundred species of mosqui-
toes have been described. Of these only the genus Anopheles transrhits
malaria to man; though in India, Ross found that Culex transmits a
form of malaria to sparrows. These two common genera are easily
distinguishable. In Culex the wings are clear; in Anopheles they are
spotted with brown. In Culex when resting, the axis of the body
forms a curved line, the insect presenting a hump-backed appearance;
in Anopheles the axis forms a straight line. Culex has short maxillary
palpi, while in Anopheles they are almost as long as the proboscis. The
note of the iemale Anopheles is several tones lower than that of Culex,
and only the female is bloodthirsty, by the way. As regards eggs,
larvae and pupae, the two genera differ greatly. The eggs of Culex are
laid in a mass and those of Anopheles singly; the larvae of Culex hang
from the surface film of a pool at an angle of about forty-five degrees,
252 ENTOMOLOGY
while those of Anopheles are almost parallel with the surface of the
water in which they Uve.
The bite of an Anopheles is not necessarily injurious, of course, unless
the insect has had recent access to a malarious person. Anopheles may
be present where there is no malaria. On the other hand, it has been
found impossible to prove that malaria exists where there are no Anoph-
eles mosquitoes. Finally, fevers are sometimes diagnosed as malarial
which are not so.
Possibly the malarial parasite can complete its cycle of development
in other animals than man. It is also possible that originally the mala-
rial organism was derived by mosquitoes from the stems or other parts
of aquatic plants, and that its effects on man are incidental phenomena.
Yellow Fever
From 1793 to 1900 there occurred in the United States not less than
half a million cases of yellow fever and one hundred thousand deaths
from the disease. New Orleans suffered the worst with more than forty-
one thousand deaths, followed by Philadelphia with ten thousand and
Memphis with almost eight thousand; while Charleston, New York
City and Norfolk, Virginia, lost together more than ten thousand lives.
The enormous financial loss from all the epidemics of yellow fever is
beyond exact computation; the epidemic of 1878 cost New Orleans more
than ten million dollars.
Yellow fever is now within human control ; with no thanks to those
who at first violently opposed the theory, and later denied the fact, of
its transmission by mosquitoes.
Until 1 901 yellow fever was fought energetically, but fought in the
dark. An immense amount of energy was misdirected and millions of
dollars wasted in the fight. On the supposition that bacteria were the
cause of the disease, methods of quarantine, burning and fumigation
were employed that destroyed an enormous amount of property includ-
ing valuable cargoes, and paralyzed the business and social activities of
great cities.
Official accounts of yellow fever published before 1900 often describe
the disease as being due to some insidious poison borne by the air and
introduced into the human body, probably through the respiratory
system. It was observed that the disease was often conveyed down
the wind, that it was not carried far from the nearest focus of infection,
that infection was less liable to occur in daylight than by night, and
TRANSMISSION OF DISEASES BY INSECTS 253
that cases arose on shore when the only source of infection was a ship
that had not yet touched the land. These facts and many others
which formerly involved the disease in mystery, are now quite intelli-
gible in the hght of the mosquito- theory of transmission.
Finlay's Work. — The pioneer work leading toward the control of
yellow fever was done by Dr. Charles J. Finlay, of Havana, Cuba, who
not only advocated the mosquito-theory strongly for many years, but
also inoculated by means of mosquitoes ninety human subjects, some
of whom came down with what he believed to be a mild form of yellow
fever. His valuable work prepared the way for the briUiant investi-
gations of Major Reed and his associates.
United States Yellow Fever Commission. — Major Walter Reed
was president of the board of medical ofhcers sent to Cuba in June, 1900,
to study the acute infectious diseases of the island; his associates were
James Carroll, Jesse W. Lazear and A. Agramonte.
At that time Sanarelli's theory as to the bacillary causation of yellow
fever was in favor, though Reed and Carroll has already shown that the
bacillus of Sanarelli bore no special relation to the disease. After further
investigations on this subject in Cuba, with negative results, the com-
mission "concluded to test the theory of Finlay," in Dr. Reed's words.
For this purpose General Leonard Wood, the mihtary governor of Cuba,
gave permission for experiments on human beings and granted a liberal
sum of money for the reward of volunteer subjects.
The commission succeeded in demonstrating how yellow fever is
transmitted; after that the methods of prevention to be employed were
evident.
The experiments, planned and directed by Major Reed, are models
of their kind. All possible sources of error were excluded; hence there
was no uncertainty in the interpretation of the results, the accuracy of
which has been confirmed by subsequent commissions and by many
independent investigators.
In the value of his services Major Walter Reed ranks among the
greatest benefactors of mankind. Before his death, which occurred in
1902, he received great honors for his brilliant achievements.
Experiments in Cuba. — For experimental purposes Major Reed es-
tablished a camp about four miles from Havana. To prevent the
introduction of the fever from the outside the inmates of the camp were
rigidly quarantined; non-immunes were confined to the camp or, if re-
leased, not allowed to return. In order that the study of yellow fever
might not be complicated by the presence of any other disease, a com-
2 54 ENTOMOLOGY
plete record was kept of the health of every subject; furthermore, ample
time was allowed for any possible development of the disease within the
camp before the experiments were begun. In short, the precautions
taken were so thorough that yellow fever never appeared in the camp
except at the will of the experimenters.
Harmlessness of Fomites. — In a specially constructed building,
which was screened against mosquitoes and purposely ill-ventilated,
volunteers slept for twenty nights with bedding and clothing that had
been contaminated by yellow fever patients, and tried in every other
way to contract the disease, if possible, from the fomites, or belongings,
of fever subjects; yet the health of these volunteers remained unimpaired;
though they were not immunes, for some of them were subsequently
infected artificially by means of mosquitoes.
Transmission by Transfusion. — It was found that the disease could
be conveyed to non-immunes by the subcutaneous injection of blood
taken from the veins of patients during the first three days of the disease.
Experiments with Mosquitoes. — These experiments were made at
a time of the year when there was the least chance of acquiring the dis-
ease naturally. The mosquitoes used were bred from the eggs and kept
active by being maintained at a summer temperature. From time to
time some of them were taken away to a yellow fever hospital, fed on the
blood of patients and applied to non-immunes in the camp at varying
intervals from the time of feeding. The occupants of the camp were, of
course, protected carefully from accidental mosquito bites. When a
subject came down with yellow fever as the result of an experimental
inoculation he was at once removed from the camp to a yellow fever
hospital.
In a mosquito-proof building a single room was divided into two
compartments simply by means of a partition of wire netting. On one
side of the screen infected mosquitoes were liberated; and a brave non-
immune, who had been in quarantine for thirty-two days, entered the
compartment, allowed himself to be bitten several times, and contracted
the disease. In the opposite compartment, free from mosquitoes, non-
immunes slept with perfect safety ; and the other room became harmless
as soon as the mosquitoes were removed.
In another experiment the subject acquired the disease by thrusting
his arm into a jar of infected mosquitoes. Eighteen non-immunes were
inoculated, ten of them successfully. It was demonstrated that yellow
fever is transmitted by the bite of a mosquito, and in no other way
except by the artificial injection of diseased blood. The mosquito can
TRANSMISSION OF DISEASES BY INSECTS
255
obtain infected blood from a patient during only the first three days of
his disease; in other words, the patient is no longer a menace to other
persons after three days from the time when he comes down with yellow
fever, which is from three to six days after the bite.
After biting a patient the mosquito cannot convey the infection until
at least twelve days have elapsed; thereafter it can transmit the disease
for certainly six weeks and possibly eight weeks.
Dr. James Carroll allowed himself to be bitten by an infected mos-
quito and consequently suffered a severe attack of yellow fever. He
recovered from this, but was left with an affection of the heart from
which he died in 1907.
Dr. Lazear failed to acquire the disease artificially, early in the
course of the experiments; but a little later, while visiting yellow fever
patients in a hospital, was bitten by a mosquito which he deliberately
allowed to remain on his hand. Five days later he came down with
yellow fever, which caused his death. His life was a sacrifice for the
benefit of the human race.
Yellow Fever Mosquito.— The mosquito that transmits this fever
is Aedes argenteus {Aedes calopus, Stegomyia fasciata) and no other
species is as yet known to be concerned in the disease. A. argenteus is
limited to warm regions; at a temperature less than 68° F. the eggs do not
hatch, and below 62° F. the female does not bite (Reed). The depend-
ence of the insect upon warmth for its development explains the
cessation of the disease in New Orleans in December, with a mean
temperature of 55.3° F. and in cities farther north when frost comes.
In Cuba and Brazil the fever has occurred every month in the year.
Cause of Yellow Fever. — The specific cause of yellow fever eluded
detection for many years and was regarded by many investigators as
being ultra-microscopic. The U. S. Commission produced the disease
by the injection of blood serum that had been passed through a bacteria-
proof filter. Blood from a subject in whom the disease had been pro-
duced by transfusion was capable of infecting a third person.
The weight of evidence indicated that the unknown cause of yellow
fever was an organism rather than a toxin, and in 19 19 the organism was
discovered by Noguchi to be a spirochaete, which he named Leptospira
icteroides. During his investigations in Guayaquil Noguchi succeeded
in isolating this spirochaete from the blood of patients and from mos-
quitoes as well. He obtained pure cultures of the parasite by inoculat-
ing guinea pigs with blood from patients, and was able to produce the
disease by inoculation in guinea pigs, dogs and marmosets.
256 ENTOMOLOGY
Following his discovery, Dr. Noguchi, of the Rockefeller Institute
for Medical Research, prepared from the organisms a vaccine, which
has been administered to many thousand persons with results that are
reported to be distinctly encouraging.
Control of Yellow Fever. — The preventive measures based upon the
facts learned by the U. S. Army Commission were wonderfully suc-
cessful. In February, 1901, Major W. C. Gorgas began a campaign to
eradicate the disease in Havana. His efforts were directed against
mosquitoes. Every case of fever had to be reported promptly to the
authorities. Then the patient was isolated and all the rooms in the
building and in neighboring houses fumigated and the doors and
windows screened. Standing water in which mosquitoes might develop
was drained or treated with petroleum, and water tanks and barrels
were screened.
In September, 1901, the last case of yellow fever arose in Havana,
where the disease had prevailed for 1 50 years, with an annual mortality
of 500 to 1600 or more. Cases are now and then brought into Havana
from Mexico or Central America but are treated under screens in the
regular hospitals with impunity.
Yellow Fever in New Orleans. — In 1905 the last epidemic of yellow
fever occurred in New Orleans. It might have been checked at its
inception had not the authorities adopted a policy of secrecy in regard
to the presence of the disease. The city was freed from the fever before
frost came, by the same methods that had proved successful in Cuba;
but not without organized work of the most strenuous kind on the part
of the citizens, under the direction of the U. S. Public Health and
Marine-Hospital Service. At present the yellow fever mosquito is
said to be a rarity in Louisiana owing to the vigorous measures enforced
in its suppression throughout the state.
Fever in the Canal Zone. — The Panama Canal zone was formerly
one of the most unhealthful places on earth, chiefly on account of the
prevalence of malaria and yellow fever. When the United States ac-
quired the zone in 1904 it was realized that the first step toward building
the great canal was to protect the health of all those immediately con-
cerned in the undertaking, and the sanitation of the isthmus was placed
in charge of one eminently quaHfied for the work. Colonel W. C. Gorgas.
He adapted the methods he had used in Cuba to the conditions
existing on the isthmus, with the result that every year the death rate
decreased until in 1908 it became, among eight thousand white
Americans living there, 9.72 per thousand, "a rate no higher than for a
TRAXs;\rissi(>x of diseases by insects 257
similar population in the healthiest localities in the United States, and
much lower than that for most parts of the country." The Sanitary
Department has succeeded in driving yellow fever from the isthmus and
in checking malaria and other diseases to such a degree that the canal
zone is no longer an unhealthful place.
After serving as Surgeon General of the United States Army from
1 9 14 to 19 1 8, W. C. Gorgas entered the service of the International
Health Board, and was organizing an international campaign against
yellow fever at the time of his death in London, July 4, 1920.
General Gorgas attained international preeminence for his ability
in organizing and conducting operations of magnitude against insect-
borne diseases. On account of his services in the protection of human
life his assistance was sought by foreign nations, and he received higHl ^
honors. . • /\
Typhoid Fever rv r**
Ski
The specific cause of typhoid fever is Bacillus typhosus. In bBte^""
human body this bacillus occurs chiefly in the intestines; but also in ofieQ *
urinary bladder and usually in the blood of infected persons.
The excreta of typhoid subjects contain the virulent bacilli; an(^s,|
some persons, even after recovery, continue to be "chronic carriers" of
the disease for many years.
Transmission. — The typhoid bacillus is introduced into the human
system by eating or drinking. Most epidemics are due to infected
water and many to milk; occasionally the disease is acquired from raw
vegetables or from oysters contaminated with sewage. Often the
bacillus is conveyed to food by human hands and possibly it is some-
times carried by dust, cockroaches or ants; but there is no doubt that
the disease is transmitted by certain flies, particularly the true house
fly, Muse a domes tica, which is by far the commonest fly found generally
in houses, and becomes a serious menace to health during epidemics of
typhoid fever.
The house fly is well adapted by its structure and habits to carry
bacteria. The adults often feed on substances contaminated with
typhoid or other bacteria and these infected substances cling readily
to the hairs of the insect, especially those of the feet, and to the pro-
boscis. The larvse develop chiefly in horse manure, but also in other
kinds of excreta, some of which may contain virulent typhoid
bacilli.
250 ENTOMOLOGY
Transmission by Flies. — During the Spanish- American war typhoid
fever occurred in every American regiment and raged in many of
the concentration camps, in consequence of which a special commission
was appointed to investigate the origin and spread of the disease in the
army. A report by one of the members of the commission, Doctor
Vaughan, presents the following conclusions:
"a. Flies swarmed over infected fecal matter in the pits and then
visited and fed upon the food prepared for the soldiers at the mess tents.
In some instances where lime had recently been sprinkled over the con-
tents of the pits, flies with their feet whitened with lime were seen
walking over the food.
"6. Officers whose mess tents were protected by means of screens
suffered proportionally less from typhoid than did those whose tents
were not so protected.
"c. Typhoid fever gradually disappeared in the fall of 1898, with
the approach of cold weather, and the consequent disabling of the fly.
"It is possible for the fly to carry the typhoid bacillus in two ways.
In the first place, fecal matter containing the typhoid germ may adhere
to the fly and be mechanically transported. In the second place, it is
possible that the typhoid bacillus may be carried in the digestive organs
of the fly and may be deposited with its excrement."
Similar conclusions in regard to the agency of flies in the spread of
enteric fever among troops have been reached also by investigators in
Bermuda, South Africa and India.
Firth and Horrocks fed house flies on material contaminated with
Bacillus typhosus and then obtained cultures of the bacillus from objects
to which the flies had access. In another experiment they obtained
cultures from the heads, bodies, wings and legs of such flies. Other
investigators have obtained Bacillus typhosus from flies captured in
rooms occupied by typhoid cases.
Faichnie caught flies in a place where there was an outbreak of ty-
phoid fever, held them on a sterilized needle and passed them through a
flame until legs and wings were scorched; after which he obtained the
typhoid bacillus from the mashed bodies of the flies, the bacilli having
been present in the ahmentary tract, without doubt.
Faichnie also obtained cultures of Bacillus typhosus from the intes-
tines of flies which had developed from larvae fed on feces containing the
bacillus.
Jordan states that the bacilli survive the passage of the ahmentary
canal of the fly.
TRANSMISSION OF DISEASES BY INSECTS 259
Ficker recovered typhoid bacilli from flies twenty-three days after
they had been infected.
In fact, a great amount of evidence has accumulated proving that
flies transmit not only the bacilli of typhoid fever, but many other
bacteria, and often in enormous numbers. For example, Esten and
Mason in their study of the sources of bacteria in milk, collected and
examined flics from stables, pig-pens, houses and other places, and found
an average of 1,222,570 bacteria per fly; the majority of these being
objectionable kinds of bacteria.
Musca Domestica. — A single female of the common house fly lays
in all some six hundred eggs. In midsummer, in Washington, D. C,
the eggs hatch in about eight hours; the larval period is from four to
five days and the pupal period five days, making the cycle about ten
days in length. In cooler parts of the season the cycle requires more
time and in warm climates it may be as short as eight days. The
number of generations in Washington is probably not more than
nine (Howard).
Control. — One of the best baits for flies in houses is formalin, which
is poisonous to flies but harmless to man. This is prepared by diluting
formaldehyde with five or six times as much water and exposing it in
shallow dishes, the addition of a little sugar or milk making the solution
more attractive to flies, which drink it and quickly die. Pyrethrum is
efl'ective against flies, but only when it is pure and has been kept from
exposure to the air. Pyrethrum, the chief basis of all the common
insect powders, is applied by being puffed through a bellows or by being
burned. The powder may be moistened and shaped into cones which
when lighted at the top burn slowly and give off fumes that are suffocat-
ing to insects.
Dr. Howard estimates that more than ten million dollars are spent
every year in screening houses in the United States. Another enormous
sum is spent for fly papers and fly traps. The efficient way to deal with
the fly problem, however, is to prevent the insects from breeding, Ex-
crementitious substances should be enclosed in such a way as to prevent
the access of flies, or should be treated in a way to kill the larvae therein;
one of the simplest methods of treating stable manure being to spread
it out to dry, since the maggots cannot develop without moisture.
For detailed information on everything of importance relating to
the house fly, and particularly on the mitigation of the fly-nuisance by
concerted action in communities, Dr. Howard's admirable book on the
house fly should be consulted.
26o ENTOMOLOGY
Plague
In the ancient history of Europe epidemics of plague occupy a large
place. For many years this pestilence has thrived in China and India,
and following an outbreak in 1894 in Hong Kong, the plague reached
the western hemisphere for the first time, appearing in Brazil, Argentina
and other South American countries, in Mexico and San Francisco.
The cause of plague is Bacillus pestis, an organism abundant in the
secretions and excretions of plague-stricken animals.
Three varieties of the disease are distinguished as follows:
(i) the bubonic, in which the bacilli cause enlargements of lymphatic
glands ;
(2) the septiccBmic, characterized by the presence of large numbers
of bacilli in the blood and highly virulent;
(3) the pneumonic, in which the respiratory organs are affected, the
sputum showing the bacilli in enormous numbers; this form, relatively
rare, is the most fatal.
Transmission. — Plague is primarily a disease of rats, an epidemic
of plague in these animals having often been observed to precede as
well as accompany an epidemic among human beings. The disease
affects also mice, cats, dogs, calves, sheep, pigs, ducks, geese and many
other animals.
Though rats and other of the lower animals may contract the septi-
caemic type of the disease from feeding on parts of animals killed by
plague or on cultures of Bacillus pestis, the disease is commonly trans-
mitted among rats neither by contact nor through the atmosphere, but
by means of fleas. Healthy rats in association, with diseased rats do
not become infected as long as fleas are excluded; but a transfer of fleas
from the latter to the former starts the disease. By various experi-
ments the Indian Plague Commission demonstrated the important part
played by rat-fleas in the transmission of plague. Zirolia found that
the bacilli even multiply in the mid-intestine of the flea, retaining their
virulence for a week or more. Bacot found that the European rat-flea
{Ceraiophyllus fasciatus) remained infective, when isolated from a
host, for forty-seven days.
The weight of evidence, both observational and experimental,
shows that plague is transmitted from rats to man by several species
of fleas and also by bedbugs. Verjbitski, whose experiments on this
subject were particularly precise and thorough, found that plague can
be conveyed by the bites of these insects and that the opening made
TRANSMISSION OF DISEASES BY INSECTS 261
by the bite affords entrance to plague bacilli when the bodies of the
insects are crushed or when the infected feces are introduced by the
rubbing or scratching of the wound.
The species of rat-flea most common in the orient is the cosmo-
politan "plague flea," Xenopsylla cheopis.
In the United States the most common rat flea is Ceratophyllus
j'asciatus. The common cat and dog flea, Clenocephalus canis, affects
rats as does the human flea, Pulex irritans; and all these species are
known to bite man.
Plague in San Francisco. — Plague, long dreaded in American sea-
ports, Anally entered San Francisco in 1900, killed 114 persons in the
next four years, became dormant and broke forth again, with violence,
in 1907. The city, just beginning to recover from the great fire of the
year before, was in a frightful sanitary condition and most of the popu-
lation, engaged in the work of reconstruction, paid little attention to
the deaths from plague and at first gave little aid toward the suppression
of the disease. As may be imagined, the campaign against the dis-
ease undertaken by the U. S. Public Health and Marine-Hospital
Service was carried on in the face of great odds. It was, however, con-
ducted most efficiently and successfully under the command of Dr.
Rupert Blue (later Surgeon-General), who wisely attacked the disease
by attacking the rat population.
The labor involved in starving out the rats, trapping or poisoning
them, and making buildings rat-proof by the use of concrete or sheet
iron, was immense; but the undertaking was nevertheless carried to a
successful conclusion. More than one million rats were killed and the
disease was checked.
In California plague affects ground squirrels, which doubtless con-
tract the disease from the rats that use the runways of the squirrels in
the fields.
Trypanosomiases
Some of the diseases known as trypanosomiases are among the dead-
liest that affect man and other vertebrates, and pathogenic trypano-
somes — the organisms causing these diseases — have received an
immense amount of study during recent years.
Trypanosomes. — The organisms under consideration are flagellate
protozoans. A typical trypanosome, for example, T. lewisi (Fig. 274)
of the rat, is essentially an elongated cell, tapering at each end, serpen-
262
ENTOMOLOGY
tine in form and with no definite cell-wall. A round or oval nucleus is
present, also a peculiar chromatin body situated often near the poste-
rior end of the cell and termed the hlepharoplast. Along one side of the
cell is a delicate protoplasmic contractile membrane, the undulating
membrane, along the edge of which is a marginal cord, which arises by-
growth from the hlepharoplast and is continued beyond the anterior
end of the cell as a vibratile flagellum.
Asexual reproduction is by means of a longitudinal division of the
cell body, preceded by division of the flagellum, hlepharoplast and
nucleus, the nucleus dividing amitotically. In
regard to the existence of sexual stages, or
gametes, the results of investigators seem to
be inconclusive as yet.
In a film of fresh blood under the microscope,
any active trypanosomes in the field of view
attract attention as centers of commotion among
the red blood corpuscles, which are pushed aside
by the lashing, twisting and other movements of
the trypanosomes.
The nutrition is by means of osmosis. Try-
panosomes have not been seen to attack erythro-
cytes, but according to MacNeal and Novy
haemoglobin is useful if not indispensable to
them.
All five classes of vertebrates serve as hosts
for trypanosomes, of which more than seventy
species have received names. Most of these
species are carried from one vertebrate host to
another by means as yet unknown, but about
20 per cent, are known or suspected to be
transmitted by an intermediate invertebrate host. Thus trypano-
somes of frogs are conveyed by leeches ; pigeons are infected by mos-
quitoes, rats by sucking lice and fleas, and many mammals through the
agency of blood-sucking flies of the genus Glossina, and probably also
by Stomoxys and certain Tabanidee.
Tsetse Flies. — The name tsetse fly, originally limited to Glossina
morsitans (Muscidse) is now used for any of the fifteen known species
of the genus. These flies are a little larger than the common house fly
{Musca domestica) . Their wings, in the resting position, overlap exactly
(Fig. 275) instead of being separated at the tips. The proboscis pro-
2 74. — Trypano-
soma lewisi. b, hlepharo-
plast; /, flagellum; m,
marginal cord; w. nucleus;
tt, undulating membrane.
Greatly magnified.
TRANSMISSION OF DISEASES BY INSECTS
263
Fig.
275. — Tsetse fly, Glossina
morsilans. X 2}^^.
jects forward, and is stout, owing to the ensheathing palpi; the base of
the labium forms a prominent bulb. These are the more conspicuous
characters that serve to distinguish tsetse flies from other blood-sucking
flies with which they might be confused.
The mode of reproduction as described by Brauer is similar to that
of the group of parasitic flies known as Pupipara. The fly produces a
full-grown larva, which at once creeps to
some resting place and forms a black
puparium.
Tsetse flies frequent hot, humid regions,
near bodies of water, and are restricted to
shaded situations, never occurring on the
open plains. Both sexes are bloodthirsty
but bite only during the daytime as a rule;
though they may bite at night when the
moonlight is bright. Travelers take advan-
tage of the habits of the fly to journey by
night; spending the day in an open unin-
fested place.
Nagana. — The colon'zation of South
Africa was greatly retarded by nagana, a disease invariably fatal to
the horse, donkey and dog, and usually fatal to cattle, but not affect-
ing man. Livingstone and other explorers in regions where nagana is
prevalent record their having been bitten by tsetse flies thousands of
times with no result other than a slight irritation.
Bruce was the first to prove the identity of nagana and tsetse-fly
disease and to demonstrate the role of the fly in the transmission of the
disease. His investigations, begun in Zululand in 1894, are of funda-
mental importance and have given an immense stimulus to the study
of trypanosomes.
After finding that no bacteria were concerned in nagana, Bruce dis-
covered trypanosomes in the blood of cattle affected with the disease.
He inoculated their blood into healthy horses and dogs and in a few days
the blood of these animals was teeming with trypanosomes. Then he
took healthy animals from the mountain on which he had located his
headquarters down into the "fly country;" there they contracted the
tsetse-fly disease and showed in their blood trypanosomes indistinguish-
able from those of nagana.
Horses taken into the fly country but not allowed to eat or drink
there, took the disease; furthermore, supplies of grass and water brought
264
ENTOMOLOGY
from the fly country and fed to healthy horses failed to convey the
disease.
Then the influence of the fly was tested. Tsetse flies caught in the
lowland, carried to the mountain and placed at once on healthy animals
gave rise to the disease; but the flies never retained the power of infect-
ing a healthy animal for more than forty-eight hours after feeding upon
a sick animal. Thus wild flies, kept without food for three days and
then fed on a healthy dog, never gave rise to the disease. The fly alone
transmitted the disease; and this by means of trypanosomes adhering
to the proboscis either inside or out. Bruce found
these organisms in the digestive tract also, but
with no change in their form.
He discovered further that buffaloes, antelopes
and many other wild animals carried the parasite
in their blood, and was able by injecting this
blood to transmit the disease to healthy domesti-
cated animals. The parasites were never numer-
ous in the blood of their wild hosts, however, and
the latter seemed to be unaffected by their pres-
ence. The ''big game" of Africa serves, gener-
ally speaking, as a reservoir for supplies of
trypanosomes.
The species of parasite that Bruce studied is
named Trypanosoma hrucei (Fig. 276). The flies
concerned are Glossina morsitans, G. pallidipes and
G.fusca, particularly the first two, the distribution
of which coincides with that of nagana.
No certain remedies for the disease are yet known. Human serum
injected into infected animals causes the trypanosomes to disappear,
at least, temporarily; but this fact is of more scientific interest than
practical importance. The precaution of traveling by night is often
adopted. Creolin and some other substances rubbed on animals
serve to repel the flies, and the smoke of encampments drives them away.
The protection of horses by means of screens is of course effective.
Human Trypanosomiasis. — Sleeping sickness is most prevalent in
the Congo basin, whence it has spread rapidly in equatorial Africa, where
it kills about fifty thousand natives every year. The reported cases of
recovery are so extremely rare that the mortality is placed at one
hundred per cent.
In the first stage of the disease, marked by the appearance of
-Trypano-
FiG. 276
S07na brucei. Greatly
magnified.
TRANSMISSION OF DISEASES BY INSECTS 265
trypanosomes in the blood, negroes show no symptoms as a rule, though
whites are subject to fever. The symptoms may appear as early as
four weeks after infection or as late as seven years.
In the second stage trypanosomes appear in the cerebro-spinal fluid
and in large numbers in the lymphatic glands, those of the neck, axillae
and groins becoming enlarged. There is tremor of the tongue and
hands, drowsiness, emaciation and mental degeneration. The drowsi-
ness passes into periods of lethargy which become gradually stronger
until the patient becomes comatose and dies. Some victims do not
sleep excessively, but are lethargic, and "profoundly indifferent to all
going on around them."
There is some disagreement among authors as to the precise effects
of trypanosomes on human tissues and organs, but the evidence indi-
cates at least that trypanosomes produce a toxin which sets up irrita-
tions of the lymphatic glands in general and those of the brain in
particular. Many of the symptoms of trypanosomiasis are traceable
primarily to inflammation of the lymphatics of the nervous system.
The specific cause of sleeping sickness is T. gambiense, discovered in
1 901 by Forde and named by Button. Two eminent English investi-
gators of sleeping sickness, Button and TuUock, sacrificed their lives to
the. disease they were studying.
As the result of the labors of many investigators, human trypano-
somiasis is now well understood. Bruce and Nabarro demonstrated by
means of inoculation experiments with monkeys that T. gambiense is
transmitted chiefly, if not solely, by a tsetse fly, Glossina palpalis.
They and Greig showed that the distribution of the disease in Uganda
coincided with that of the fly. In some regions where the fly is present
the disease is unknown; which means simply that cases of the disease
have not yet been introduced.
Notwithstanding the great activity in the study of this disease no
good remedy for it has been found. Wise travelers in tropical Africa
take every precaution against being bitten by tsetse flies. Much effort
is being exerted to check the spread of the disease among the natives in
some of the infected regions; chiefly by removing patients from the fly
region, by screening dwellings or by building them away from the dainp
and marshy areas where the flies breed.
FiLARIASIS
The first disease found to be transmitted by an insect was filariasis,
the subject of important investigations by Manson, Bancroft and others.
266 ENTOMOLOGY
This disease of tropical and subtropical regions is caused by a thread-
worm, or nematode, known as Filaria bancrofti, which occurs in the
blood of man and of several of the lower animals as a slender larva
(microfilaria) about one-quarter of a millimeter in length. At night
these larvse swarm in the peripheral circulation, from which they are
taken into the ahmentary canal of a blood-sucking mosquito (chiefly
Culex quinquefasciatus) . In the mid-intestine of the mosquito the larva
escapes from its sheath and penetrates into muscular tissue, where it
grows and develops for two or three weeks, after which it goes to some
other part of the mosquito's body, often to the base of the proboscis,
whence the larvae are carried into the blood of some vertebrate host,
there to develop to sexual maturity.
The larvae are often common in human blood without seeming to
injure the host in any way, but the adults (three or four inches long and
often found in groups) and ova that have escaped from the parent
female sometimes obstruct the lymphatic canals and cause enormous"
swellings of feet, legs, arms or other parts of the human body; this
condition being known as elephantiasis.
Typhus
War and typhus have always gone hand in hand. Crowded and
uncleanly conditions in camps and prisons are most favorable to the
propagation of the disease.
Recent History. — The last scourge of typhus in Serbia began in
October, 19 14 among Austrian prisoners, who spread the disease over
the country. No adequate means of checking the disease existed, and
in January, 191 5 the epidemic was raging. In April there were 9,000
deaths per day; the total mortahty for the first five months of 191 5
being more than 100,000. This epidemic was checked largely by the
energetic efforts of Dr. R. P. Strong and his fellow- workers.
Syria suffered from typhus in 191 6, with more than 1,000 deaths
daily. In Roumania, 1916-1919, the mortahty was 26,000. Mexico
City had 11,000 cases of typhus in December, 1915. In the United
States the disease occurs now and then in a small way, but especially
among immigrants.
Cause. — The specific cause of typhus can not as yet be named with
certainty. It may be a certain spirochaete discovered in 191 7' by
Futaki, who found it in the liver and urine of typhus victims, as well as
in a monkey after inoculation with infected human blood. Others
have ascribed the disease to bacilli.
TRANSMISSION OF DISEASES BY INSECTS 267
Transmission. — Whatever the organism may be, the fact is now
established that typhus is transmitted by human lice. Nicolle, Comte
and Conseil, working in northern Africa (1909), conveyed the disease
by the injection of human blood to a chimpanzee; then from the
chimpanzee to a macaque monkey; and, by means of human body lice,
from this animal to other monkeys. Drs. Ricketts and Wilder
performed similar experiments in Mexico City (19 10) with similar
results. They found that monkeys kept free from lice remained
healthy, but contracted the disease after inoculation by means of body
lice which had fed on the blood of typhus patients. They showed also
the strong probability that infection is transmitted through the eggs
to the next generation of lice, which through this indirect infection can
cause typhus in monkeys and presumably in man also. It has been
found that both the body louse {Pediculus corporis) and the head louse
{P. capitis) transmit typhus, but bedbugs and fleas are not impHcated.
The brilliant work of Dr. H. T. Ricketts was cut short by his death,
in 191 o, from typhus contracted during his experiments.
Control. — A typhus patient is harmless as a source of contagion in
the absence of human Hce, the agents of transmission. Lice, as is well
known, crawl readily from man to man in crowded quarters, and inhabit
the clothing as well as the body, particularly the underclothing, the
seams of which may contain the eggs in immense numbers. Eradica-
tion of lousiness means freedom from typhus. During the World War,
Great Britain, France and Germany were successful in protecting their
armies from the ravages of typhus by the use of methods, often elabo-
rate, directed against the Hce, or "cooties." These methods, which
are generally known, consisted of (i) the thorough cleansing of the
surface of the human body; (2) the disinfection of clothing and other
belongings, and of the living quarters, by various physical or chemical
processes.
Relapsing Fever
Relapsing or recurrent fever is less fatal than typhus, but Hke the
latter is conveyed by lice (though not exclusively) and accompanies
war. The disease has often raged in Europe; the last epidemic, early
in the recent war, being exceptionally severe in Serbia.
The cause of relapsing fever is the genus Spirochceta, of which
different species produce various types of the disease in different parts
of the world.
268 - ENTOMOLOGY
Nicolle and his colleagues demonstrated in 1913 that the European
and North African form of the disease is transmitted by the body
louse, and the head louse as well, though not by their bites. When
the lice are crushed and the infected contents of their bodies rubbed into
wounds made by the lice, or into abrasions of the skin, or are transferred
as by the fingers to a mucous membrane, such as the conjunctiva of
the eye, the disease is produced.
It was proved that, in some instances at least, infection could be
transmitted through the eggs to the lice of the next generation. The
European form of the disease may be conveyed by the bedbug also,
according to some investigators. In central Africa a common tick
is the agent of transmission, and in Mexico and Central America ticks
and bedbugs are suspected.
Trench Fever
One of the most disabling diseases in the Great War was trench
fever. The experiments made by British and American investigators
in 19 1 8 proved that this disease also is transmitted by the body louse,
Pediculus corporis. The physical cause of the fever is conveyed in the
feces of the lice and inoculation occurs through scratching by the victim,
and possibly also by means of punctures made by the hce. The specific
cause of trench fever is, however, not actually known as yet.
Other Diseases
Cholera is undoubtedly transmitted by flies. As long ago as 1899
Dr. Nuttall wrote: "The body of evidence as to the role of flies in the
diffusion of cholera is, I believe, absolutely convincing."
Dysentery is probably carried by fhes, as Dr. Orton and others have
inferred from their experiments.
Spillman and Haushalter, as well as several others, examined flies
that had fed on tubercular sputum and found in the intestinal contents
and in the dejections of these flies the bacilli of tuberculosis.
Dr. F. T. Lord summarizes his important investigations on this
subject as foflows:
" I. Flies may ingest tubercular sputum and excrete tubercle bacilli,
the virulence of which may last for at least fifteen days.
"2. The danger of human infection from the tubercular fly-specks
is by the ingestion of the specks on food. Spontaneous liberation of
TRANSMISSION OF DISEASES BY INSECTS 269
tubercle bacilli from fly-specks is unlikely. If mechanically disturbed,
infection of the surrounding air may occur."
If it is true that tuberculosis can be transmitted by means of food,
as experiments with some of the lower animals seem to indicate, the
house fly is evidently a factor that must be reckoned with in the fight
against this disease.
There is conclusive evidence that Egyptian ophthalmia is trans-
mitted by flies and it is highly probable that certain other infections
of the eye are conveyed by the same means.
The bacillus of the deadly disease anthrax can be transmitted by
tabanid flies and stable flies, Stomoxys.
Dr. H. Graham and others have proved that dengue is conveyed by
two species of mosquitoes, the common house mosquito of the tropics
{Culex quinquejasciatus) and the yellow fever mosquito {Aedes argenteus).
Phlebotomus fever of Mediterranean regions and India is known to
be carried by a sand iiy, Phlebotomus; and the peculiar Oroya fever of
Peru is possibly transmitted by a fly of the same genus.
There is partial proof that the destructive kala-azar in India is
disseminated by the common Indian bedbug.
Tropical sore is probably spread by flies of some kind.
In Ceylon, the skin disease known as yaws is conveyed by the com-
mon house fly, Musca domestica; and in the West Indies, probably by
common flies of the genera Oscinis and Sarcophaga.
In 191 2 Professor M. J. Rosenau and Dr. C. T. Brues announced
that they had succeeded in transmitting infantile paralysis (polio-
myelitis) to monkeys by means of the stable fly, Stomoxys calcitrans,
and their results were confirmed by Dr. J. F, Anderson. Whether
this is the usual means of transmission among human beings it remains
to be determined. There is also some experimental evidence that the
disease may be carried by the bedbug.
Rocky Mountain spotted fever was proved by Ricketts in 1906
to be conveyed by two or more common species of wood ticks of the
genus Dermacentor.
Smith and Kilborne demonstrated that the destructive Texas fever
of cattle, due to a protozoan parasite, is transmitted by a common tick
Margaropus annulatus. The adoption of methods of pasturing that
enable cattle to avoid the ticks has been highly successful.
CHAPTER X
INTERRELATIONS OF INSECTS
Insects in general are adapted to utilize all kinds of organic matter
as food, and they show all gradations of habit from herbivorous to carniv-
orous. The many forms that derive their food from the bodies of other
insects may conveniently be classed as predaceous or parasitic.
Predaceous Insects. — Among Orthoptera, Mantidae are notably
predatory, their front legs (Fig. 64, C) being well fitted for grasping and
killing other insects. The predaceous odonate nymphs have a peculiar
hinged extensible labium with which to gather in the prey. The adults
catch with surpassing speed and precision
a great variety of flying insects, mostly
small forms, but occasionally butterflies of
considerable size. The eyes of a dragon
fly are remarkably large; the legs form a
spiny basket, probably to catch the prey,
which is instantly stripped and devoured,
these operations being facilitated by the
» excessive mobility of the head. The
f' hemipterous families Corixidae, Notonec-
% tidae (Fig. 227), Nepidae, Belostomidae
(Fig. 23), Naucoridae (Fig. 64, D) Redu-
viidae and Phymatidae are predaceous, with
raptorial front legs and sharp beaks.
Some of the Pentatomidae (Fig. 277) are
of considerable economic value on account
of their predaceous habits. Most of the Neuroptera feed upon other
insects. The Myrmeleon larva (ant-lion) digs a funnel-shaped pitfall,
at the bottom of which it buries itself to await the fall of some
unlucky ant. The Chrysopa larva (aphis-lion) impales an aphid on
the points of its mandibles and sucks the blood through a groove
along each mandible (Fig. 46, E), the maxilla fitting against this
groove to form a closed channel. Several families of Coleoptera
are almost entirely predaceous. Among aquatic beetles, Dytiscidae
are carnivorous both as larvae and imagines, Gyrinidag subsist chiefly
270
Fig. 277. — Nymph of Podisus
maculivenlris sucking the blood
from a clover caterpillar, Colias
philodice. Natural size.
INTERRELATIONS OF INSECTS 27 1
upon disabled insects, but occasionally eat plant substances, and
Hydrophilidas as larvae catch and devour other insects, though some
of the beetles of this family {H. triangularis, for example, Fig. 229) feed
largely if not entirely upon vegetation. Of terrestrial Coleoptera, the
tiger beetles (Cicindelidae) are strictly predaceous upon other insects.
The Cicindela larva lives in a burrow in the soil and lies in wait for
passing insects; a pair of hooks on the fifth segment of the abdomen
serves to prevent the larva from being jerked out of its burrow by the
struggles of its captive. The large family Carabidae is chiefly predace-
ous; these "running beetles," both as larvae and adults easily overtake
and capture other terrestrial insects. The Carabidae, are by no means
exclusively carnivorous, however, for many of them feed to some extent
upon fungus spores, pollen, ovules, root-tips and other vegetable matter,
as Forbes has found ; Harpalus caliginosus eats the pollen of the ragweed
in autumn ; Galerita janus eats caterpillars and occasionally the seeds
of grasses; but Calosoma appears to be strictly carnivorous, feeding
chiefly upon caterpillars and being in this respect of considerable
economic importance. As a whole, Carabidae prefer animal food, as
appears from the fact that when canker worms, for instance, are unusu-
ally abundant these form a correspondingly large percentage of carabid
food, the increase being compensated by a diminution in the amount
of vegetable food taken. (Forbes.) Coccinellid larvae (excepting Epi-
lachna, which eats leaves) feed almost entirely upon plant lice and con-
stitute one of the most effective checks upon their multiplication; the
beetles eat aphides, but also fungus spores and pollen in large quantities.
Though Lepidoptera are pre-eminently phytophagous, the larva of
Feniseca tarquinius is unique in feeding solely upon plant lice, particular-
ly the woolly Schizoneura tessellata of the alder. Among Diptera,
Asilidae, Midaidae, There vidae and Empididae are the chief predaceous
families. Asilidae (robber-flies) ferociously attack not only other flies,
but also beetles, bumblebees, butterflies, and dragon flies; as larvae
they feed largely upon the larvae of beetles. Many of the larvas of
Syrphidae prey upon plant lice, and the larvae of Volucella feed in Europe
on the larvae of bumblebees and wasps. Of Hymenoptera, the ants are
to a great extent predaceous, attacking all sorts of insects, but particu-
larly soft-bodied kinds; while Vespidae feed largely upon other insects,
though like the ants they are fond of the nectar of flowers and the juices
of fruits.
Parasitic Insects. — Though very many insects occur as external
parasites on the bodies of birds and mammals, very few occur as such on
272
ENTOMOLOGY
the bodies of other insects; one of the few is Braula ccBca, a wingless
dipteron found on the body of the honey bee.
A vast number of insects, however, undergo their larval develop-
ment as internal parasites of other insects, and most of these parasites
belong to the two most specialized orders, Diptera and Hymenoptera.
The larvae of Bombyliidae feed upon the eggs of Orthoptera and upon
larv£e of Lepidoptera and Hymenoptera. Tachinidae are the most
important dipterous parasites of other insects and lay their eggs most
frequently upon caterpillars; the larvae bore into their victim, develop
Fig. 278. — Megarhyssa atrata, drilling in tree trunk.
Macnamara.
Natural size. — From Charles
within its body, and at length emerge as winged insects. These parasites
often render an important service to man in checking the increase of
noxious Lepidoptera.
The great majority of insect parasites — many thousand species —
belong to the order Hymenoptera, constituting one of the primary
divisions of the order. They are immensely important from an eco-
nomic standpoint, particularly the Ichneumonidae, of which more than
ten thousand species are already known. Our most conspicuous
ichneumonids are the two species of Megarhyssa, M. atrata (Fig. 278),
and M. lunator with their long ovipositors (three inches long in
lunator, and four to four and three-quarters inches in atrata) . Mega-
rhyssa bores into the trunks of trees in order to reach the burrows of
INTERRELATIONS OF INSECTS
273
another large hymenopteron, Tremex columba (Fig. 30), upon whose
larvae the larva of Megarhyssa feeds.
The enormous family Braconidoe, closely related to Ichneumonidae,
is illustrated by the common Apanteles coiigregaius, which lays its eggs
in the caterpillars of various Sphingidae. The parasitic larvae feed upon
the blood and possibly also the fat-body of their host, and at length
emerge and spin their cocoons upon the exterior of the caterpillar (Fig.
279), sometimes to the number of several hundred. Species of Aphidins
transform within the bodies of plant lice, one to each host, and the imago
cuts its way out through a circular opening with a correspondingly
Pig. 279. — A tomato worm, Proloparce sexla, bearing cocoons of the parasitic Apanteles
congregatus. Natural size.
circular lid. Chalcididae, of which some four thousand species are
known, are usually minute and parasitic; though some are phytopha-
gous, for example, species of Harmolita (Isosoma) which live in wild or
cultivated grasses, and the clover seed-midge Bruchophagus funebris.
Chalcids affect a great variety of insects of one stage or another, such
as caterpillars, pupas, cockroach eggs, plant lice and scale insects;
while some of them develop in cynipid galls, either upon the larvae of
the gall-makers or upon the larvae of inquilines. Giard in France reared
more than three thousand chalcids {Copidosoma truncatellum) from a
single caterpillar of Plusia. Proctotrypidae are remarkable as parasites.
Most of them are minute; indeed, this family and the coleopterous family
Trichopterygidae contain the smallest winged insects known — species
but one-third or one-fourth of a millimeter long. A large proportion
274 ENTOMOLOGY
of the Proctotrypidae are parasitic in the eggs of other insects or of
spiders, several sometimes developing in the same egg; others affect
odonate nymphs and coleopterous or dipterous larvae, while several
species have been reared from itonidid and cynipid galls, and
many proctotrypids are parasites of other parasitic insects — in other
words, are hyper parasites.
Hyperparasitism. — Not only are primary parasites frequently
attacked by other, or secondary, parasites, but tertiary parasitism is
known to occur in a few instances, and there is some reason to believe
that even the quaternary type exists among insects, as in the following
case.
The caterpillar of Hemerocampa leucostigma defoliates shade trees
in the northeastern United States. An enormous increase of this
species in the city of Washington in 1895 was attended by a
corresponding increase of parasitic and predaceous species, and this unu-
sual opportunity for the study of parasitism was made the most of by
Dr. Howard, from whose admirable paper these facts are taken.
The primary parasites of H. leucostigma numbered 23 species — 17
Hymenoptera and 6 Diptera; of the hyperparasites (all hymenopterous)
13 were secondary, 2 and probably 5 were tertiary, and one of these
(Asecodes alhitarsis) may under certain conditions prove to be a quater-
nary parasite. To illustrate — The ichneumon Pimpla inquisitor, an
important primary parasite of lepidopterous larvas, lays its eggs in cater-
pillars of H. leucostigma; its larvae suck the blood of their host and at
length spin their cocoons within the loose cocoon of the Hemerocampa.
These cocoons have yielded a well-known secondary parasite, the chalcid
Dibrachys houcheanus. Now another chalcid, Asecodes alhitarsis, has
been seen to issue from a pupa of this Dibrachys, thus establishing terti-
ary parasitism. Furthermore, it is quite possible that Dibrachys
itself is a tertiary parasite, in which event the Asecodes might become
a parasite of the quaternary order.
Economic Importance of Parasitism. — If a primary parasite js
beneficial, its own parasites are indirectly injurious, generally speaking;
while those of the third and the fourth order are respectively beneficial
and injurious. The last two kinds are so rare, however, as to be of no
practical importance from an economic standpoint. The first two kinds
are of immense economic importance, particularly the primary parasites.
" Outbreaks of injurious insects," says Howard, " are frequently stopped
as though by magic by the work of insect enemies of the species. Hub-
bard found, in 1880, that a minute parasite, Tricho gramma pretiosa, alone
INTERRELATIONS OF INSECTS 275
and unaided, almost annihilated the fifth brood of the cotton worm in
Florida, fully ninety per cent, of the eggs of this prolific crop enemy
being infested by the parasite. In 1895, in the city of Washington,
more than ninety-seven per cent, of the caterpillars of one of our
most important shade-tree pests [Hemerocampa, as just mentioned]
were destroyed by parasitic insects, to the complete relief of the city the
following year. The Hessian fly, that destructive enemy to wheat
crops in the United States, is practically unconsidered by the wheat
growers of certain states, for the reason that whenever its numbers
begin to be injuriously great its parasites increase to such a degree as to
prevent appreciable damage.
"The control of a plant-feeding insect by its insect enemies is an ex-
tremely complicated matter, since, as we have already hinted, the
parasites of the parasites play an important part. The undue multipli-
cation of a vegetable feeder is followed by the undue multiplication of
parasites, and their increase is followed by the increase of
hyperparasites. Following the very instance of the multiplication of
the shade tree caterpillar just mentioned, the writer [Howard] was able
to determine this parasitic chain during the next season down to quater-
nary parasitism. Beyond this point, true internal parasitism probably
did not exist, but even these quaternary parasites were subject to
bacterial or fungus disease and to the attacks of predatory insects.
*'The prime cause of the abundance or scarcity of a leaf-feeding
species is, therefore, obscure, since it is hindered by an abundance of
primary parasites, favored by an abundance of secondary parasites
(since these will destroy the primary parasites), hindered again by an
abundance of tertiary parasites, and favored again by an abundance of
quaternary parasites."
Entomologists have made many attempts to import and propagate
insect enemies of various introduced insect pests, and some of their
efforts have been crowned with success, as was notably the case when
Novius cardinalis, a lady-bird beetle, was taken from Australia to Cali-
fornia to destroy the fluted scale.
Form of Parasitic Larvae. — The peculiar environment of parasitic
larvae is responsible for profound changes in their organization. These
larvae, in general, are apodous, the body is compact and the head is more
or less reduced, sometimes to the merest rudiment. These characters,
occurring also in such dipterous larvae as Hve in a mass of decaying or-
ganic matter, and again in those hymenopterous larvae whose food is pro-
vided by the mother or by nurses, are to be attributed to the presence
276 ENTOMOLOGY
of a plentiful supply of food, obtainable with little or no exertion, and
indicate, not primitive simplicity of organization, but a high degree of
speciahzation, as we have said before. The embryonic development of
parasitic larvae is frequently highly anomalous, as appears in the chapter
on development.
Maternal Provision. — Excepting several families of Hymenoptera
and the Termitidae, few insects make any special provision for the wel-
fare of the young beyond laying the eggs in some appropriate situation.
Many insects, as walking-sticks (Phasmidae) and some butterflies
{Argynnis) simply drop their eggs to the ground, leaving the young to
shift for themselves. Most insects, however, instinctively lay their
eggs in situations where the larva is sure to find its proper food near at
hand. Thus various flies and beetles deposit their eggs on decaying
animal matter, butterflies and moths are more or less restricted to par-
ticular species of plants, and parasitic Hymenoptera to certain species of
insects. The beetles of the genus Necrophorus go so far as to bury the
body of a bird, mouse or other animal in which the eggs are to be laid;
and in this instance the male assists the female in undermining and
afterward covering the body. A similar co-operation of the two sexes
occurs in the scarabaeid beetles known as "tumblebugs," a pair of which
may often be seen rolling along laboriously a ball of dung which is to
serve as larval food. The female mole-cricket {Gryllotalpa) is said to
care for her eggs and even to feed the young at first.
Hymenoptera display all degrees of complexity in regard to maternal
provision. Tenthredinidae simply lay their eggs on the proper food
plants or else insert them into the tissues of the plants. Sphecina make
a nest, provision it with food and leave the young to care for themselves.
Queen wasps and bumblebees go a step further in feeding the first larvae
and carrying them to maturity. Finally, in the honey bee the care of
the young is at once relegated by the queen to other individuals of the
colony, as is also the case among ants.
Some of the most elaborate examples of purely maternal provision
are found among the digger wasps and the solitary wasps; these in-
stances are highly interesting, involving as they do an intricate co-ordi-
nation of many reflex actions — as appears in the discussion of insect
behavior.
Among the Sphecina, or digger wasps, the female makes a nest by
burrowing into the ground, by mining into such pithy plants as elder or
sumach, or else by plastering bits of mud together. The nest is provi-
sioned with insects or spiders which have been stung in such a way as
INTERRELATIONS OF INSECTS 277
usually to be paralyzed, without being actually killed. The various
species of Sphecina frequently select particular species of insects or
spiders as food for the young. Pepsis Jormosa (Pompilidaj) uses taran-
tulas for this purpose; Sphecius speciosus (Bembecidie) stores her nest
with a cicada; Nyssonidae pick out certain species of Membracidae ;
mud-daubers (Sphecidae) use spiders; and other families of Sphecina
capture bees, beetles, plant lice or other insects, as the case may be.
The solitary wasps (Eumenidae) are similar to the digger wasps in habits.
Of the solitary bees, Megachile is well known for its habit of cutting
pieces out of rose leaves; it uses oblong pieces to form a thimble-shaped
tube which, after being stored with pollen and nectar, is plugged with a
circular piece of leaf. The larval cells are made either in tunnels ex-
cavated in wood by the mother or else in cracks or other chance cavities.
One of the carpenter bees, Ceratina dupla, which builds in the hollow
stem of a plant a series of larval cells separated by partitions, is said by
Comstock to watch over her nest until the young mature.
The transition from the solitary to the social habit is indicated in the
lifq-histories of wasps and bumblebees, where a solitary queen founds
the colony but soon relegates to other individuals all duties except that
of egg-laying. The social insects will now be considered.
Termites
Though popularly known as "white ants," the termites are quite
different from true ants, being indeed not very far removed from the
most primitive insects. In view of the extreme contrast in structure
and development between termites and ants, it is remarkable that the
two groups should have much the same kind of complex social
organization.
Classes of Termites.^ — In general, four principal kinds of adults are
produced in a community of termites, namely — workers, soldiers, fertile
males and fertile females.
The workers (Fig. 280, A) which are ordinarily the most numerous,-
are of either sex, but their reproductive organs are undeveloped. A
worker ant or .bee, is, however, always a female. The termite workers,
as the name impHes, do most of the work; they make the nest, provide
food, feed and care for the young and the royal pair, and attend to
many other domestic duties.
The soldiers, like the workers, are of either sex, with undeveloped
sexual organs. With monstrous mandibles and head (Fig. 280, B),
278
ENTOMOLOGY
their chief duty apparently is to defend the colony, though they fre-
quently fail to do so.
The winged males. and females (Fig. 280, C) which are sexually ma-
FiG. 280. — Various forms of Reticulitermes lucifugus. A, adult worker; B, soldier; C,
perfect winged insect; D, perfect insect after shedding the wings; E, young complementary
queen; F, older complementary queen. Enlarged. — After Grassi and Sandi.^s.
ture, swarm from the nest and mate. After the nuptial flight the pair
burrow into some crevice and shed the wings, which break off each along
a peculiar transverse suture, leaving four triangular
stumps (Fig. 280, D). The king and queen found
a new colony and may live for several years, shelt-
ered in a special chamber; the queen, meanwhile,
becoming enormously distended (Fig. 281) with eggs
and almost incapable of locomotion. The prolificacy
of the queen is astonishing; she can lay thousands
of eggs, sometimes at the rate of sixty per minute.
She is the nucleus of the colony, and should she
become incapacitated, is replaced by one or more
substitute queens, which have been developed to
meet the emergency; similarly, a substitute king is
matured upon occasion. These substitutes (Fig.
280, E) differ from the primary pair in having
nymphal wing pads in place of the remains of func-
tional wings.
In regard to Termopsis angusticollis, in California,
Dr. Heath says that if only one of the royal pair be
destroyed usually only one substitution form is
developed, but when both perish, from ten to forty
substitutes appear, according to the size of the colony.
In all, three types of reproductive forms are recognized : ^r^/ form,
Fig. 281. — Queen
of Termes obesus.
Natural size. — After
Hagen.
INTERRELATIONS OF INSECTS 279
true kings and queens, with functional wings or their remnants; second
form, substitute males or females, with short wing pads; third form,
ergatoid, or worker-like, males or females, without wings, this type
being rather rare.
In certain tropical species there are two types of soldiers, and two of
workers; so that adults of either sex may occur under seven different
forms in the same colony.
Origin of Castes. — Grassi maintains that all the forms are ahke at
birth except as regards sex, and that the differences between worker
and soldier, which are independent of sex, depend probably upon nutri-
tion. Grassi attributes all the diversities of caste, except the sexual
ones, to the character and amount of the food.
C. B. Thompson states that at hatching there are two kinds of
nymphs (i) the "reproductive," which develop into the fertile castes,
and (2) the ''worker-soldier" nymphs, which become the sterile castes;
these two types being distinguishable by internal differences in the brain,
compound eyes, and sex organs.
Food.— The food of termites is of six kinds: (i) wood; (2) matter
emitted from the oesophagus or rectum, termed respectively stomodasal
and proctodaeal food; (3) cast skins and other exuvialstuflf ; (4) the bodies
of their companions; (5) saliva; (6) water. Of these the proctodaeal
food is the favorite. Nymphs receive at first only saliva; later they get
stomod^eal and proctodaeal food until, finally, they are able to eat wood
— the staple food of a termite.
American Species. — Our common termite is Reticulitermes jiavipes,
which occurs throughout the United States, excavating its galleries in
decaying logs, stumps or other dead wood. The nuptial flight of this
species takes place in spring, when the two sexes swarm in numbers that
are sometimes enormous. One swarm, as recorded by Hagen, appeared
as a dense cloud, and was being followed and attacked by no less than
fifteen species of birds, among which were robins, bluebirds and sparrows;
some of the robins were so gorged to the mouth with termites that their
beaks stood open. Though plenty of winged females are said to occur
in the swarming season, the true queen of R. fiavipes is extremely rare,
the queen usually found being evidently, from her undeveloped wings,
a substitute queen.
The European species Reticulitermes lucifugus has been found
recently in Massachusetts. Most species of termites occur in warm
climates, however. North of Mexico thirty-six species are known,
28o
ENTOMOLOGY
most of which have come from the south, and more species are liable to
be introduced at any time (Banks).
Architecture. — While many termites simply burrow in dead wood,
other species construct more elaborate nests. A Jamaican species
builds huge nests in the forks of trees, with covered passageways leading
to^the ground.
In parts of Africa and Australia, where they are free from disturbance,
Fig. 282. — Termite mound, Kimber-
ley type, Australia. — After Saville-
Kent.
Fig. 2S3. — Mound of the "com-
pass" termite of North Australia. —
After Saville-Kent.
termites erect huge mounds, frequently six to ten and sometimes
eighteen or twenty feet high, with galleries extending as far below the
surface of the ground as they do above it. These immense structures
(Fig. 282) consist chiefly of earth, cemented by means of some secretion
into a stony clay, with which also much excrementitious matter is mixed ;
they are pyramidal, columnar, pinnacled or of various other forms, ac-
cording to the species, and are perforated by thousands of passages and
chambers, while there are underground galleries extending away from
the mound to a distance of often several hundred feet.
INTERRELATIONS OF INSECTS 201
An extraordinary type of mound is constructed by the "compass"
or "meridian," termites of North Australia, for their wedge-shaped
mounds (Fig. 283), commonly eight or ten feet high, though sometimes
as high as twenty feet, are directed north and south with surprising accu-
racy. By means of this orientation the exposure to the heat of the sun is
reduced to the minimum, as occurs also in the case of many Austrahan
plants, the leaves of which present their edges instead of their faces to
the sun.
More than one species of termite may inhabit a single nest; in one
South African nest Haviland found live species of termites and three of
ants. The widely distributed genus Eutermes is essentially a group of
inquiline, or guest, species. Termite mounds afford shelter to scor-
pions, snakes, lizards, rats, and -even birds, some of which nest in them.
The Australian bushmen hollow out the mounds to make temporary
ovens, and even eat the clay of which they are composed, while hill-
tribes of India are accustomed to eat the termites themselves, the
flavor of which is said to be delicious.
Ravages. — In tropical regions the amount of destruction done by
termites is enormous, and these formidable pests are a constant source
of consternation and dread. They emit a secretion that corrodes
metals and even glass, while anything made of wood is simply at their
mercy. Always avoiding the light, they hollow out floors, rafters or
furniture, leaving only a thin outer shell, and as a result of their in-
sidious work a chair or a table may unexpectedly crumble at a touch.
Jamestown, the capital of St. Helena, was largely destroyed by termites*
(1870) and had to be rebuilt on that account.
In the United States and Europe few species of termites occur, and
they do little injury as compared with the tropical species; though our
common Reticulitermes flavipes occasionally damages woodwork, books,
plants, etc., in an extensive way, particularly in the Southern states.
Termitophilism. — Associating with termites are found various
other arthropods, mostly insects. The relations of these termitophilous
forms to the termites are, so far as is known, similar to those described
beyond between myrmecophilous species and ants.
Honey Bee
For more than three thousand years the honey bee has been almost
unique among insects as an object of human care and study. It was
highly prized by the old Greeks and Romans (as appears from the writ-
282
ENTOMOLOGY
ings of Aristotle, 330 B. C, and Cato, about 200 B. C.) and actually
worshiped as a symbol of royalty by the ancient Egyptians, through
whose papyri and scarabs the honey bee may be traced back to the time
of Rameses I., or 1400 B. C.
The honey bee, unhke domesticated animals, is so little dependent
upon man that it readily returns to a wild hfe. Under many dis-
tinct races, which are due largely to human intervention. Apis niel-
lifera is widely distributed over the earth.
Castes.— The species comprises three kinds of individuals: queen,
drone and worker (Fig. 284) . The workers are females with an atrophied
reproductive system. They constitute the vast majority in any colony
and are the only kind that is commonly seen out of doors. Upon the
industrious workers falls the burden of the labor; they build the comb,
Fig. 2f
A B C
-The honey bee, Apis mellifera. A, queen; B, drone; C, worker. Natural size.
nurse the young, gather foCd, clean and repair the nest, guard it from
intruders, control larval development, expel the drones — briefly, the
workers alone are responsible for the general management of the com-
munity. Though hibernating workers Hve eight or nine months, the
other workers live but from five to twelve weeks.
The term queen is, of course, a misnomer, for the government of
the hive is anything but monarchical. The chief duties of the queen,
or mother, are simply to lay eggs and to lead away a swarm. She is able
to deposit as many as 4,000 eggs in twenty-four hours. After a single
mating, the spermatozoa retain their vitality in the spermatheca of the
queen for three or four years — the lifetime of a queen. The males, or
drones, apart from their occasional sexual usefulness, are of little or no
service, and their very name has become an expression for laziness.
The Comb. — Wax, of which the comb is built, is made from honey or
sugar, many pounds (twenty, according to Huber) of honey being re-
quired to make one pound of wax. The workers, gorged with nectar,
cling to one another in a dense heated mass until the white films of wax
INTERRELATIONS OF INSECTS
>83
appear underneath the abdomen (Fig.. 104) ; these are transferred to the
mouth, as described on page 229, and are masticated with a fluid,
secreted by cephalic glands, which alters the chemical composition of
the wax and makes it plastic.
The workers now contribute their wax to form a vertical, hanging
septum, on the opposite sides of which they proceed to bite out pits —
the bottoms of the future cells — using the
excavated wax in making the cell walls. The
bottom of each cell consists of three rhombic
plates (Fig. 285, A), and the cells of one side
interdigitate with those of the other side (Fig.
285, B) in such a way that each rhomb serves
for two cells at once. Wax is such a precious
substance that it is used (instinctively, how-
ever) always with the greatest economy; the
cell walls, are scraped to a thinness of 3-^80 or
}ioo of an inch, and nowhere is more wax used
than is suflBcient for strength; one pound of wax
makes from 35,000 to 50,000 worker cells. The
cells, at first circular in cross section, become
hexagonal from the mutual interference of
workers on opposite sides of the same wall;
the form is, however, by no means a regular
hexagon in the mathematical sense, for it is difficult to find a cell with
errors of less than 3 or 4 degrees in its angles. (Cheshire.) Worker
cells are one fifth of an inch in diameter, while the larger cells, destined
for drones or to hold honey, are one quarter of an inch across.
To strengthen the edges of cells or to fill crevices, the workers use
propolis, the sticky exudation from the buds or leaf axils of poplar, fir,
horse-chestnut or other trees; though they will utilize instead such arti-
ficial substances as grease, pitch or varnish. As winter approaches, the
bees apply the propolis liberally, making their abode tight and
comfortable.
Larval Development. — When the brood cells are ready, the queen,
attended by workers, lays an egg in each cell and has no further con-
cern as to its fate. After three days the egg discloses a footless grub
(Figs. 286, 287) which depends at first upon the milky food that bathes
it and has been supplied from the mouths of the worker nurses. Later
the larva is weaned by its nurses to pollen, honey and water. As the
stomach and the intestine of the larva do not communicate with each
Fig. 285. — A, bases of
comb cells; B, section of
comb. Somewhat e n-
larged. — After Cheshire.
284
ENTOMOLOGY
Other, the excretions of the larva cannot contaminate the surrounding
nutriment, and are retained until the final molt. Five days after
hatching, the larva spins its cocoon,
the workers having meanwhile cov-
ered the larval cells with a porous
cap of wax and pollen (Fig. 287)
and on the twenty-first day after
the egg was laid the winged worker
bee cuts its way out, assisted in
this operation by the ever-attentive
nurses. Now, after acquiring the
use of its faculties, the newly
emerged bee itself assumes the
duties of a nurse, but as soon as
its cephalic nursing glands are
exhausted it becomes a forager.
This account applies to the worker;
the three kinds of individuals differ
Fig. 286.— Comb of honey bee, showing in respect to the number of days
the insect in various stages. At the right required for development, as
are large queen cells. — After Benton. ^ _ '^ '
appears in the following table,
from Phillips:
Queen. .
Worker.
Drone. .
Egg.
Larva.
Pupa.
Total
3
s'A
jH
16
3
6
12
21
3
6}^
I4>2
24
The cells in which queens develop (Fig. 286) are quite different from
worker or drone cells, being much larger, more or less irregular in form,
and vertical instead of
horizontal; they are ^^l P
attached usually to the
lower edge of a comb or
else to one of the side
edges.
Other Facts.— The
entire organization of the
honey bee has been pro-
foundly modified with ref-
erence to floral structure; the life of the bee is wrapped up in that of
the flower. The more important structural adaptations of bees in
Fig. 287. — Honey bee. /, feeding larva; p, pupa;
s, spinning larva. — After Cheshire.
INTERRELATIONS OF INSECTS 285
relation to flowers have been described, as well as many of their sensory
peculiarities; there remain to be added, however, some other items of
interest, chosen from the many.
A colony of bees in good condition at the opening of the season con-
tains a laying queen and some 30,000 to 40,000 worker bees, or six to
eight quarts by measurement. Besides this there should be four, five,
or even more combs fairly stocked with developing brood, with a good
supply of honey about it. Drones may also be present, even to the
number of several hundred.
Ordinarily the queen mates but once, flying from the hive to meet
the drone high in the air, when five to nine days old usually. Seminal
fluid sufficient to impregnate the greater number of eggs she will deposit
during the next two or three years (sometimes even four or five years)
is stored at the time of mating in a sac— the spermatheca, opening into
the egg-passage.
The liquid secreted in the nectaries of flowers is usually quite thin,
containing, when just gathered, a large percentage of water. Bees suck
or lap it up from such flowers as they can reach with their flexible, suck-
ing tongue, 0.25 to 0.28 inch long. This nectar is taken into the honey
sac, located in the abdomen, for transportation to the hive. Besides
being thin, the nectar has at first a raw, rank taste, usually the flavor
and odor peculiar to the plant from which gathered, and these are fre-
quently far from agreeable. To make from this raw product the health-
ful and delicious table luxury which honey constitutes — "fit food for the
gods" — is another of the functions peculiar to the worker bee. The
first step is the stationing of workers in lines near the hive entrances.
These, by incessant buzzing of their wings, drive currents of air into and
out of the hive and over the comb surfaces. If the hand be held before
the entrance at such a time a strong current of warm air may be felt
coming out. The loud buzzing heard at night during the summer time
is due to the wings of workers engaged chiefly in ripening nectar. In-
stead of being at rest, as many suppose, the busy workers are caring for
the last-gathered lot of nectar and making room for further accessions.
This may go on far into the night, or even all night, to a greater or less
extent, the loudness and activity being proportionate to the amount and
thinness of the liquid. Frequently the ripening honey is removed from
one set of cells and placed in others. This may be to gain the use of
certain combs for the queen, or possibly it is merely incidental to the
manipulation the bees wish to give it. When, finally, the process has
been completed, it is found that the water content has usually been re-
286 ENTOMOLOGY
duced to lo or 12 per cent., and that the disagreeable odors and flavors,
probably due to volatile oils, have also been driven off in a great measure,
if not wholly, by the heat of the hive, largely generated by the bees.
During the manipulation an antiseptic (formic acid) , secreted by glands
in the head of the bee, and possibly other glandular secretions as well
have been added. The finished product is stored in waxen cells above
and around the brood nest and the main cluster of bees, as far from the
entrance as it can be and still be near to the brood and bees. The work
of sealing with waxen caps then goes forward rapidly, the covering being
more or less porous. Each kind of honey has its distinctive flavor and
aroma, derived, as already indicated, mainly from the particular blos-
soms by which it was secreted, but modified and softened by the
manipulation given it in the hives. The last three paragraphs are taken
from Benton's useful manual.
The phenomenon of "swarming" results from the tremendous re-
productive capacity of the queen, though it is immediately an instance
of positive phatotropism, as Kellogg has shown. Accompanied by most of
the workers, the old queen abandons the hive to establish a new colony.
The workers that remain behind have provided against this contingency,
however, and the departed queen is soon replaced by a new one.
Determination of Caste.- — The difference between queen and worker
depends solely upon nutrition, both forms being derived from precisely
the same kind of egg. To produce a queen, a large cell of special form
is constructed, and its occupant, instead of being weaned, is fed almost
entirely upon the highly nutritious secretion which worker grubs receive
only at first and in limited quantity. This nitrogenous food, the prod-
uct of cephalic glands, develops the reproductive system in proportion
to the amount received. Drone larvae get much of it, though not so
much as queens, while an occasional excess of this "royal jelly" is
beheved to account for the abnormal appearance of fertile workers.
Parthenogenesis, or reproduction without fertilization, is known to
occur in the bee, as well as in various other insects. The always un-
fertilized eggs of workers produce invariably drones, as do also unfertil-
ized eggs of the queen.
Dzierzon's Theory. — The much discussed theory of Dzierzon, pro-
posed more than seventy-five years ago, is essentially as follows: (i)
the queen is able "at will" to lay either male or female eggs; (2) all
the eggs in the ovaries would develop into males if unfertihzed, but
fertihzed eggs produce females.
It is a matter of common observation that the queen is able to lay
INTERRELATIONS OF INSECTS 287
female eggs in worker or queen cells, and male eggs in drone cells; but
the means by which she exercises control over the fertilization of the
eggs is not understood.
It is known that unfertilized eggs produce always drones, and at
present it is generally beheved by geneticists that drones never
come from fertilized eggs. The principal reasons for this opinion
are these: (i) if a pure-bred queen of one race is crossed with a drone
of another race, the female progeny (workers or queens) have hybrid
characters, but the male offspring have only characters of the maternal
race; (2) eggs from worker or queen cells contain spermatozoa; those
from drone cells do not.
Bumblebees
Familiar as the bumblebees are, their habits have been little studied
in this country, though in England ''bumblebees" have formed the
subject of an interesting volume by Sladen. The queen hibernates and
in spring starts a colony, utilizing frequently for this purpose the
deserted nest of a field mouse or sometimes the burrow of a mole or
gopher. The queen lays her eggs in a small mass of pollen mixed with
nectar (Putnam) . The larvae eat out cavities in the mass of food and
when full grown spin silken cocoons, from which the imago cuts its
way out; the empty cocoon being subsequently used as a receptacle for
honey. At first only workers are produced and they at once relieve the
queen of the duties of collecting nectar and pollen, caring for the young,
etc. The workers are of different sizes, the smaller ones being nurses
or builders and the larger ones foragers — the kind commonly seen out of
doors. In the latter part of summer both males and females are pro-
duced, but when severe frost arrives, the old queen, the workers and the
males succumb, leaving only the young queens to survive the winter.
Social Wasps
The Social Wasps constitute the family Vespidas, of which we have
three genera, namely, Vespa, Polistes and Polybia, the last genus being
represented by a single Californian species.
Vespa.— Some species of Vespa, as V. maculata, make a nest which
consists of several tiers of cells protected by an envelope (Fig. 288), at-
taching the nest frequently to a tree; other species, as germanica and
vulgaris, make a nest underground. The paper of which the nests are
288 ENTOMOLOGY
composed is manufactured from weather-worn shreds of wood, which
are torn off by the mandibles and then masticated with a secreted fluid
which cements the paper and makes it waterproof.
A solitary queen founds the colony in spring; she starts the nest,
lays eggs, feeds the young and brings forth the first workers; these then
relieve her — continue the building operations, collect food, nurse the
young; in short, assume the burden of the labor. In the latter part of
summer, fertile males and females appear and pairing occurs. Though
the statement has often been made that only the young queens survive
^^
Fig. 288. — Nest of wasp, Vespa macidata. A, outer aspect; B, with envelope cut away to
show combs. Greatly reduced.
the winter, there is some reason to believe that not only the queens but
also males and workers may hibernate successfully in the nest.
The larvae are fed at first, by regurgitation, upon the sugary nectar
of flowers and the juices of fruits, and later upon more substantial food,
such as the softer parts of caterpillars, flies, bees, etc., reduced to a pulp
by mastication; occasionally wasps steal honey from bees.
The workers, as is usual among social Hymenoptera, are modified
females, incapable of reproduction as a rule, though the distinction be-
tween worker and queen is not nearly so sharp among wasps as it is
among bees. Worker eggs are said to be parthenogenetic and to pro-
duce only males. The males, unhke those of the honey bee, are active
laborers in the colony. In the tropics there are wasps that form per-
manent colonies, store honey and swarm, after the manner of honeybees.
Polistes.— The preceding description of Vespa applies equally well
to our several species of Polistes, except that the nest of Polistes is a
INTERRELATIONS OF INSECTS 289
single comb hanging by a pedicel and without a protecting envelope.
Miss Enteman, who has carefully studied the habits of Polistes, finds
that the larva spins a lining as well as a cap for its cell, by means of a
fluid from the mouth, and that the adults emerge after a pupal period of
three weeks, males and females appearing (in the vicinity of Chicago)
in the latter part of August and early in September.'
Ants
The habits of ants have engaged the serious attention of some of the
most sagacious students of the phenomena of life. Any species of ant
presents innumerable problems to the thoughtful investigator and about
five thousand species, subspecies and varieties of ants have been
described.
A large part of our knowledge of the habits of these remarkable
insects has been obtained by the use of artificial formicaries, which are
easily constructed and have yielded important results in the hands of
Lubbock, Forel, Janet, Wasmann, Fielde, Wheeler and other well-
known students of ants. We have an important comprehensive volume
on these insects by Wheeler.
Castes. — In a colony of ants three kinds of individuals are produced
as a rule: males, females and workers, the last being sexually imperfect
females.
The males and females swarm into the air for a nuptial flight, after
which the males die, but the females shed their wings and enter upon a
new and prolific existence, which may last for many years; a queen of
Lasius niger was kept alive by Lubbock for nine years, and one oi Formica
fusca, fifteen years, and then its death was due to an accident.
The workers live from one to seven years, according to the same
authority. They constitute the vast majority in any colony and are the
familar forms that so often command attention by their industry and
pertinacity. In some species certain of the workers are known as
soldiers; these may be recognized by their larger head and mandibles.
Pol3miorphism. — Ants and termites surpass all other insects in
respect to the number of forms under which a single species may occur.
In some species of ants several types of workers exist; these are distin-
guished by structural peculiarities of one kind or another, which
possibly indicate special functions, for the most part as yet unas-
certained. Furthermore, the sexual individuals are not necessarily
winged; some or all of them may be wingless, especially the females.
290 ENTOMOLOGY
These wingless males and females are termed ergatoid, on account of
their resemblance to workers.
As to how these various forms are produced, very little is known.
Probably, as among bees, workers and queens are produced from the
same kind of eggs, which have been fertilized, and the differences
between worker and queen and between workers themselves may be due
to the quality and quantity of the food that is supplied to the larvae
by their nurses. As in bees, the parthenogenetic eggs laid by abnormal
workers may produce males, as Forel, Lubbock and Miss Fielde have
found; or they may produce normal workers, as Reichenbach and Mrs.
A. B. Comstock have found to be the case in Lasius niger. Wheeler
points out the possibility of the inheritance of worker characters through
the male offspring of workers.
Larvae. — The numerous eggs laid by one or more queens are taken
in charge by the young workers, through whose assiduous care the help-
less larvae are carried to maturity. The nurses feed the larvae from their
own mouths, clean the larvae, and carry them from one place to another
in order to secure the optimum conditions of temperature, moisture, etc.
When a nest is broken open, the workers seize the larvae and pupae and
hurry into some dark place. The pupa is either naked or else enclosed
in a cocoon, spun by the larva.
Nests. — The species of the tropical genus Eciton do not make nests
but occupy temporarily any suitable retreat which they may happen to
find in the course of their wanderings. Ants in general know how to
utilize all sorts of existing cavities as nests; they make use of crevices
in rocks and under stones or bark, the holes made by bark-beetles, hollow
stems or roots, plant-galls, fruits, etc. The extraordinary "ant-plants"
have already received special consideration.
Very many ants excavate their nests in the ground ; after a rain these
ants are especially industrious in the improvement of the nest, pressing
the wet earth into the walls of the galleries and adding probably a se-
creted fluid which acts as a cement; stones and sticks are often worked
into the walls of a nest and the mounds of ants are frequently fashioned
about blades of grass or growing herbage of whatever kind. The sub-
terranean galleries are often complex labyrinths; frequently there are
long underground passages extending out in all directions, sometimes
to aphid-infested roots of plants or, as in the case of the leaf-cutting
ants of the tropics, to trees which are destined to be attacked; special
chambers are set apart for the storage of food and others for eggs, larvae
or pupae.
INTERRELATIONS OF INSECTS 29I
Often a nest is excavated under a stone. As Forel observes, the
stone warms speedily under the rays of the sun, and in damp or cool
weather the ants are always in the highest story of the nest as soon as
the sun's warmth begins to penetrate the soil, while they go below as
soon as the sun disappears or when its heat becomes too strong. They
select stones that are neither too large nor too small to regulate the tem-
perature well, while other ants attain the same object by making the
nest under sheltering herbage or by making a mound with a hard
cemented roof.
The well-known ant-hills may consist simply of excavated particles
of soil or else, as in the huge mounds of Formica exsectoides,mz,ycontdi\n
labyrinthine passages in addition to those underground. The mounds
of this species are elaborate structures which may last a man's lifetime
at least. F. exsectoides is accustomed to form new colonies in connec-
tion with the parent nest; McCook found in the Alleghanies no less than
1,600 nests, forming a single enormous community with hundreds of
millions of inhabitants, hostile to all other colonies of ants, even those
of the same species. This ant covers its mound with twigs, dead leaves,
grass and all sorts of foreign material, and is said to close the exits of the
nest with bits of wood at night and in rainy weather, removing them in
the morning or when the weather becomes favorable.
As Forel says [translation]: "The chief feature of ant architecture,
in contradistinction to that of the bees and the wasps, is its irregularity
and want of uniformity — that is to say, adaptability, or the capacity of
making all the surroundings and incidents subserve the purpose of at-
taining the greatest possible economy of space and time and the greatest
possible comfort. For instance, the same species will live in the Alps
under stones which absorb the rays of the sun; in a forest it will live in.
warm, decayed trunks of trees; in a rich meadow it will live in high,
conical mounds of earth." Some species construct peculiar pasteboard
nests, as Lasius fuliginosus of Europe and tropical species of Cremasto-
gaster; and others spin silk to fasten leaves together, as Polyrhachis of
India and (Ecophylla of tropical Asia and tropical Africa, the silk being
probably a salivary secretion, according to Forel.
Habits in General. — The habits of ants are an inexhaustible and
ever-fascinating subject of study to the naturalist, and well repay the
most critical observation. While each species has its characteristic
habits, ants in general have many customs in common.
Thus ants of one colony exhibit, as a rule, a pronounced hostiHty.
toward ants of any other colony, even one of the same species, but
292 ENTOMOLOGY
recognize and spare members of their own colony, even after many
months of separation and though the colony may number half a million
individuals. This recognition is effected by means of an odor, dis-
tinctive of the colony and apparently inheritable. When an ant is
washed and then restored to its fellows, it is treated at first as an intru-
der and may even be killed. The same is true when the ant has been
smeared with juices from the bodies of alien ants. According to Miss
Fielde, workers of colony A, smeared with the juices from crushed ants
of colony B and then placed in colony B are received amicably, but at
once set about to destroy their hosts, Uke "wolves in sheep's clothing."
These statements apply only to workers, however, for alien larvae and
pupae are frequently captured and reared by ants, and Miss Fielde
states that kings of one colony of Stenamma when introduced into
another colony are even cordially received.
Some of the most careful students of the habits of ants agree that
these insects can communicate with one another. An ant discovers a
supply of food, returns toward the nest, meets a fellow worker, the two
stroke antennae and then both start back to the food; before long other
members of the colony swarm to the prize. It has been thought that
the odor of the food or some other odor, left by the first ant, serves as a
trail for the other ants to follow. Bethe, indeed, infers from his ex-
periments that this phenomenon is purely mechanical and involves no
psychical qualities on the part of the ants. His own experiments, how-
ever, show that one ant can inform another by means of an odor as to
the whereabouts of food — which is certainly one form of communication.
Ants avoid sunlight as a rule but prefer rays of lower refrangi-
bility to those of higher. Upon exposing ants to the colors of the spec-
trum, as transmitted through glasses of different colors, Lubbock found
that they congregated in greatest numbers under the red glass and that
the numbers diminished regularly from the red to the violet end of the
spectrum, there being very few individuals under the violet glass.
Miss Fielde, experimenting with queens, workers and young of
Stenamma fulvum piceum in an artificial nest, covered half the nest with
orange glass and half with violet. "The ants removed hastily from
under the violet as often as an interchange of the panes was made, once
or twice a day, for about twenty days. Thereafter they became indif-
ferent to the violet rays." "The plasticity of the ants is remarkably
shown in their gradually learning to stay where they were never disturbed
by me, under rays from which their instincts at first withdrew them."
Ants are sensitive not only to the different colors of the spectrum
INTERRELATIONS OF INSECTS 293
but also to the ultra-violet rays, which produce no appreciable effect
on the human retina (though they induce chemical changes) . If obliged
to choose between the two, ants prefer violet to ultra-violet rays, as
Lubbock found. If, however, the ultra-violet rays are intercepted, by
means of a screen of sulphate of quinine or bisulphide of carbon, the ants
then collect under the screen in preference to under the violet rays.
From lack of experience we can form no adequate idea as to the range
of sensation in ants or other insects. Ants can taste substances that we
cannot, and vice versa. They show no response to sounds of human
contrivance, yet many of them possess stridulating organs and organs
that are doubtless auditory; whence it may be inferred that ants can
communicate with one another by means of sounds. In rare instances
the stridulation of an ant can impress the human ear, as in a species of
Atta mentioned by Sharp.
Experiments show that ants, as well as bees and wasps, find their
way back to the nest, not by a mysterious "sense of direction," but by
remembering the details of the surroundings, and in the case of ants, by
means of an odor left along the trail.
In studying the habits of ants, the greatest care must be exercised in
order to discriminate between actions that may be regarded as purely
instinctive and those that may indicate some degree of intelligence. If
any insects show signs of intelligence, the social Hymenoptera do; but
in the study of this recondite subject, false conclusions can be avoided
only by observation and experimentation of the most critical kind.
Hunting Ants.^ — Some ants, as Formica fusca, live by the chase,
hunting their prey singly. The African "driver ants " {Anomma arcens) ,
although bhnd, hunt in immense droves, consuming all the animal refuse
in their way, devouring all the insects they meet, and not hesitating to
attack all kinds of vertebrates; these ants ransack houses from time to
time and clear them of all vermin, though they themselves are a great
nuisance to the householder. The Brazilian species of Eciton (Fig. 290,
jB, C) have similar habits and are likewise blind, or else have but a single
lens on each side of the. head. These insects hunt in armies of hundreds
of thousands, to the terror of every animate thing they come across*
They have no permanent abode, but now and then appropriate some
convenient hole for the purpose of raising a new brood of marauders.
Slave-making Ants.— It is a fact that some ants make slaves of
other species. Formica sanguinea, for example, will attack a colony of
Formica fusca, kill its active members in spite of their determined re-
sistance, kidnap the larvae and pupae and carry them home, where the
294
ENTOMOLOGY
captives receive every care, and at length, as imagines, serve their mas-
ters as faithfully as they would serve their own species. In the Alle-
ghanies, according to McCook, colonies of F.fusca occur where there are
no "red ants" {F. sanguinea) , but are hard to find where the enslaving
species occurs.
Although F. sanguinea can exist very well without slaves, Polyergus
rufescens, of Europe, is notoriously dependent upon their services, it
being doubtful whether it is capable of feeding itself. This species is
powerful as a warrior, but its mandibles are of little use, except to pierce
the head of an adversary. Strongylonotus is still more helpless, while
Aner gates (also of Europe) is said to depend absolutely upon its slaves.
Polyergus lucidus occurs in the AUeghanies, where the colonies of this
species, according to McCook, contain large numbers of the workers of
Formica schaufussi. The masters are good fighters but do no other
work, and have not been seen to feed themselves, though they may often
be seen feeding from the mouths of their slaves.
Honey Ants.— Among ants in general, the workers that stay in the
Pig. 289.-
-Honey ants, Myrmecocyslus melliger, clinging to the roof of their chamber.
About natural size. — After McCook.
nest receive food from the mouths of the foragers — a custom which has
led to the extraordinary conditions found in the "honey ants," in which
certain of the workers sacrifice their own activity in order to act as liviilg
reservoirs of food (repletes) for the benefit of the other members of the
colony. This remarkable habit has arisen independently, in different
genera of ants, in North America, Australia and South Africa, as Lub-
bock observes.
INTERRELATIONS OF INSECTS 295
The honey ant whose habits are best known, through the studies of
McCook and others, is Myrmecocystus melliger, of Mexico, New Mexico
and southern Colorado. In this species some of the workers hang slug-
gishly from the roof of their little dome-like chamber, several inches
underground, and act as permanent receptacles for the so-called honey,
which is a transparent sugary exudation from certain oak-galls; it is
gathered at night by the foraging workers and regurgitated to the
mouths of the "honey-bearers," whose crops at length become dis-
tended with honey to such an extent that the insects (Fig. 289) look
like so many little translucent grapes or good-sized currants. This
stored food is in all probability drawn upon by the other ants when
necessary.
Leaf-cutting Ants. — The most dangerous foes to vegetation in
tropical America are the several species of AUa (Fig. 290, A). Living
Fig. 290. — A, leaf -cutting ant, Alia cephaloies. B, wandering ant, Eciton drepanophorum;
C, Eciton omnivorum. Natural size. — After Shipley.
in enormous colonies and capable of stripping a tree of its leaves
in a few hours, these formidable ants are the despair of the planter;
where they are abundant it becomes impossible to grow the orange,
coffee, mango and many other plants. These ants dig an extensive
underground nest, piling the excavated earth into a mound, sometimes
thirty or forty feet in diameter, and making paths in various directions
from the nest for access to the plants of the vicinity; Belt often found
these ants at work half a mile from their nest; they attack flowers,
fruits and seeds, but chiefly leaves. Each ant, by laboring four or five
minutes, bites out a more or less circular fragment of a leaf (Fig. 291)
and carries it home, or else drops it for another worker to carry; and
two strings of ants may be seen, one carrying their leafy burdens toward
the nest, the other returning for more plunder.
The use made of these leaves has been the subject of much discus-
sion. Belt found the true explanation, but it remained for Moller to
investigate the subject so thoroughly as to leave no room for doubt.
The ants grow a fungus upon these leaves and use it as food. The bits
of leaves are kneaded into a pulpy, spongy mass, upon which the
296
ENTOMOLOGY
fungus at length appears. The food for the sake of which the ants
carry on their complex operations consists of the knobbed ends of
fungus threads (Fig. 292), and these bodies, rich in fluid, form the most
important, if not the sole food of the leaf-cutting ants. By assiduously
weeding out all foreign organisms the ants obtain a pure culture of the
fungus, and by pruning the fungus
they keep it in the vegetative con-
dition and prevent its fructification;
under exceptional circumstances,
nevertheless, the fungus develops
aerial organs of fructification of the
Fig. 291. — A, B, cuts made Fig. 292. — Fungus clumps {Roziles
in Cuphea leaves in four or five gongylophora) cultivated by ants of the
minutes by Atta discigera; genus A Ha. Greatly magnified. — After
natural size. C, Atta dis- Moller.
cigera transporting severed
fragments of leaves; reduced. —
After Moller.
agaricine type, but this species (Rozites gongylophora) has never been
found outside of ants' nests. The pecuHar clubbed threads were
produced by Moller in artificial cultures and are not spores, but prod-
ucts of cultivation. Other ants are known to cultivate other kinds
of fungi for similar purposes.
McCook has found a leaf-cutting ant {Atta fervens) in Texas, and
mentions that it cuts circular pieces out of leaves of chiefly the live-oak,
these being dropped to the ground and taken to the nest by another
set of workers. He records an underground tunnel of Atta fervens
which extended 448 feet from the nest and then opened into a path 185
feet in length; the tunnel was 18 inches below the surface on an average,
though occasionally as deep as 6 feet, and the entire route led with
remarkable precision to a tree which was being defoHated.
INTEREELATIONS OF INSECTS 297
The same observer has given also a brief account of a leaf-cutting ant
that lives in New Jersey. This species {Trachymyrmex septentrionalis)
cuts the needle-like leaves of seedling pines into little pieces, which are
carried to the nest. Two columns of workers may be seen, one com-
posed of individuals returning to the nest, each with a piece of pine
needle, the other of outgoing workers. The nest is a simple structure,
extending some seven inches underground and ending in a chamber in
which are several small pulpy balls, consisting probably of masticated
leaves. Further studies upon our own leaf-cutting ants, modeled after
the admirable studies of Moller, are much to be desired.
Harvesting Ants. — Lubbock observes that some ants collect the
seeds of violets and grasses and preserve them carefully for some purpose
as yet unknown. From such a beginning as this may have arisen the
extraordinary habits of the agricultural, or harvesting, ants, of which
some twenty species are known from various parts of the world.
The Texas species Pogonomyrmex barbatus, studied by Lincecum
and by McCook, clears away the herbage around its nest (even plants
several feet high and as thick as a man's thumb) and levels the ground,
forming a disk often lo or 12 and sometimes 15 to 20 feet in diameter,
from which radiating paths are made, from 60 to 300 feet in length.
The ants go back and forth along these roads, carrying to the nest seeds
which they have collected from the ground or else have cut from plants ;
these seeds are stored in "granaries" several feet underground and are
eventually used as food. The ants prefer the seeds of a grass, Aristida
oligantha, but the oft-repeated statement that they sow the seeds of this
"ant-rice," guard it and weed it, is denied by Wheeler.
Notwithstanding the elaborate studies of McCook upon this subject,
there still remain not a few essential questions to be answered.
Myrmecophilism. — To add to the complexity of ant-life, the nests
of ants, when at all extensive, are frequented by a great variety of other
arthropods, which on account of their association with ants are termed
myrmecophiles. Most of* these are insects, of which Wasmann has
catalogued 1,200 species, but not a few are spiders, mites, crustaceans,
etc. Though the diverse relations between myrmecophiles and ants
are but partially understood, these aliens may for convenience be con-
sidered under five groM^?>: captives^ guests, visitors, intruders dind parasites.
Captives. — Besides enslaving other species, as already mentioned,
ants make use of aphids and some coccids for the sake of their palatable
products. The attendance of ants upon colonies of plant lice is a com-
mon occurrence and one that repays careful observation. With the
298 ENTOMOLOGY
aid of a hand-lens, one may see the ants hastening about among the
plant lice and patting them nervously with the antennae until at length
some aphid responds by emitting from the end of the abdomen a glisten-
ing drop of watery fluid, which the ant snatches. This fluid, contrary
to prevalent accounts, is not furnished by the so-called honey-tubes of
the aphid, but comes from the alimentary canal; the " honey- tubes " are
glandular indeed, but are probably repellent in function. In some
instances ants give much care to their aphids, for example covering them
with sheds of mud, which are reached through covered passageways.
More than this, however, some ants actually collect aphid eggs and pre-
serve them over winter as carefully as they do their own eggs. In one
such instance Lubbock found that the aphids upon hatching, after six
months, were brought out by the ants and placed upon young shoots of
the English daisy, their proper food plant. In our own country, as
Forbes has discovered, the eggs of the corn root louse {Aphis maidira-
dicis) are collected in autumn by ants (especially of the genus Lasius)
and stored in the underground nests. In winter the eggs are taken to
the deepest parts of the nest, and on bright spring days they are brought
up and even scattered about temporarily in the sunshine; while if a nest
is opened, the ants carry off the aphid eggs as they would their own.
In spring the ants tunnel to the roots of pigeon grass and smar tweed,
seize the aphids and carry them to these roots, and later to the roots of
Indian corn. Throughout the year the ants exercise supervision over
these aphids; occasionally, as Forbes says, an ant seizes a winged louse
in the field and carries it down out of sight, and in one such instance it
appeared that the wings had been gnawed away near the body, as if to
prevent the escape of the louse. Similar relations exist also between
ants and some species of scale insects.
Guests. — Though Aphididae and Coccidae are able almost always to
live without the help of ants, there are some insects which have never
been found outside the nests of ants. Most of these insect guests are
beetles, notably Staphylinidae and Pselaphidae. The rove-beetles make
themselves useful by devouring refuse organic matter, and these scav-
engers are unmolested by the ants with which they live. A few myrme-
cophilous beetles furnish their hosts with a much-coveted secretion and
receive every attention from the ants, which clean these valuable beetles
and even feed them mouth to mouth, as the ants feed one another.
Lomechusa (Fig. 293) is one of these favored guests, as it has abdominal
tufts of hairs from which the ants secure a secreted fluid. Atemeles
(Fig. 294) is another; it solicits and obtains food from the mouth of a
INTERRELATIONS OF INSECTS
299
foraging ant as if it were an ant itself. In the Alleghanies, Atemeles
cava occurs in the nests of Formica rufa, and is much prized by this ant
on account of the fluid which the beetle secretes from glandular hairs
on the sides of the abdomen.
The beetle Claviger has at the base of each elytron a tuft of hairs,
Fig. 293. — Lomechusa strumosa being freed of mites by Dinarda dentata. — After Wasmann.
Fig. 294. — Atemeles emarginatus being fed by an ant, Myrmica scabrinodis. — After
Wasmann.
which the ants lick persistently. This beetle is blind and appears to be
incapable of feeding itself; for when deprived of ant-assistance it dies,
even though surrounded by food. These cases of symbiosis, or mutual
benefit, are well authenticated.
Visitors.— Many myrmecophilous insects are not restricted to ants'
nests, but are free to enter or to leave. This is true of such Staphylinidae
as visit formicaries simply for shelter or to feed upon detritus, and these
visitors are treated with indifference by the ants.
300
ENTOMOLOGY
Intruders. — Not so, however, with species that are inimical to the
interests of the ants, such as many species of StaphyUnidae and His-
teridae, which steal food from the ants, kill them or devour their larvae
or pupae at every opportunity. The ants are hostile to these marauders,
though the latter often escape through their agihty or else rely upon
their armor for protection. Quedius brevis and Myrmedonia, as Schwarz
observes, are soft-bodied forms which remain beside the walls of the gal-
leries or near the entrance of a nest and attack solitary ants; while
Hetcerius, which mixes with the ants, is protected by its hard and smooth
covering, under which the legs and antennae can be withdrawn. Such
an enemy is an unavoidable evil from the standpoint of an ant.
Fig. 295. — Atelura formicaria stealing food from a pair of ants. — After Janet.
Janet has described the amusing way in which an audacious species
of Atelura steals food from the very mouths of ants, As is well known,
ants are accustomed to feed one another from mouth to mouth. When
the foragers, filled with honey or other food, return to the nest, they are
solicited for food by those that have remained at home; as a forager and
a beggar stand head to head, the former disgorges small drops of food,
which are seized by the latter. While a pair of ants are engaged in this
performance (Fig. 295), and a drop of honey is being passed, the Atelura
rushes in, grabs the drop and hurries away. As might be expected,
these interlopers are constantly being chased by their victims from one
corner of the nest to another.
Parasites.^-Nematode worms occupy the pharyngeal glands of ants;
larvae of Stylops inhabit their bodies; more than thirty kinds of mites
attach themselves to the heads or feet of ants; while Chalcididae and
Proctotrypidae parasitize ants' eggs.
INTERRELATIONS OF INSECTS 3OI
Origin of the Social Habit. — Wheeler regards "trophallaxis,"
meaning exchange of nourishment, as the source of the social habit in
wasps, ants, and termites; though admitting that the phenomenon has
not been observed in the social bees. He says: "If we confine our
attention largely to the ants, I believe it can be shown that trophallaxis,
originally developed as a mutual trophic relation between the mother
insect and her larval brood, has expanded with the growth of the
colony like an ever-widening vortex till it involves, first, all the adults
as well as the brood and therefore the entire colony; second, a great
number of species of ahen insects that have managed to get a foothold
in the nest as scavengers, praedators or parasites (symphily); third,
alien social insects — i.e., other species of ants (social parasitism);
fourth, alien insects that live outside the nest and are ''milked" by
the ants (trophobiosis) ; and, fifth, certain plants which are visited or
sometimes partly inhabited by the ants (phytophily)."
CHAPTER XI
INSECT BEHAVIOR
The subject of insect behavior will be considered under three heads ;
(i) Tropisms, (2) Instinct, (3) IntelHgence.
I. Tropisms
Environmental influences, such as light, temperature or moisture,
may control the direction of locomotion of an organism by determining
the orientation of its body. The reaction of the organism under these
circumstances is known as a tropic, or tactic, reaction. A moth, for ex-
ample, flies toward a flame — is positively phototropic; a cockroach, on
the contrary, avoids the Ught — is negatively phototropic. A plant turns
toward the sun — in other words, is positively heliotropic.
An insect flies toward the Ught as inevitably and as mechanically as
a plant turns toward the sun; indeed, the two phenomena are funda-
mentally the same. Some students prefer, however, to use the term
taxis for bodily movements of motile organisms, and the term tropism
for turning movements of fixed organisms.
The study of tropic reactions has already illuminated the entire
subject of the behavior of organisms and placed it on a rational basis,
and the complex tropisms of insects offer a fresh and large field to the
investigator.
Chemotropism. — Positive and negative chemotropism, as Wheeler
observes, "are among the most potent factors in the Uves of insects."
Insects are affected positively or negatively by such substances as can
affect their end-organs of smell or taste. Positive chemotropism
enables many insects to find their food or their mates; and negative
chemotropism enables them to avoid injurious substances. This
negative reaction on the part of other organisms is made use of also by
such insects as emit repellent odors.
A maggot orients its body with reference to a source of food and then
moves toward the food just as mechanically as a moth flies to a flame.
The maggot, as Loeb maintains, is influenced chemically by the radiat-
ing diffusion from a piece of meat, and follows a line of diffusion to the
302
INSECT BEHAVIOR 303
center of diffusion in much the same way that a moth follows a ray of
light to its source. In both cases a stimulus affects muscular tissue;
the animal orients its body until the muscular tension is symmetrically
distributed, and then locomotion brings the animal to the source of the
stimulus, whether it be food or light.
The remarkable "instinctive" action of the fly in laying her eggs on
meat is due, according to Loeb, simply to the fact that both the fly and
the maggot have the same kind of positive chemotropism. Similarly
also in the case of such butterflies or other insects as lay their eggs on a
special kind of plant. It is certain that "neither experience nor voHtion
plays any part in these processes."
W. M. Barrows determined experimentally that the well-known
pomace fly, Drosophila ampelophila, is positively chemotropic to amyl
alcohol, ethyl alcohol, acetic acid, lactic acid and other chemical sub-
stances, all of which occur in fermenting fruits. The fly finds its food,
not by sight, but by smell, and when this sense is lost it reaches its food
only by accident. The olfactory sense organs that are concerned with
finding food are located in the third or terminal segment of the antenna.
When one antenna is lost and the other antenna is stimulated by food
odor, circus movements are carried out in such a way as to prove that
the fly orients normally by an unequal stimulation of the antennae.
Drosophila, when stimulated by a weak food odor, first shows random
movements, i.e., it attempts to find the food by the method of trial and
error, but as the fly passes into an area of greater stimulation, these
movements give way to a direct orientation.
Hydrotropism. — Wheeler observed that beetles of the genera Hali-
plus and Hydroporus were positively hydrotropic; that when released on
the shore from a bunch of water plants, they scrambled toward the lake,
twenty feet away. Collectors take advantage of the negative hydro-
tropism of Bembidion, Elaphrus, Omophron and other shore-dwelling
beetles by splashing the water upon the dry bank, when the beetles leave
their places of concealment and are easily caught.
It is well known that after a rain ants carry their young out into the
sunshine, though when the upper parts of the nest become too dry, the
ants transfer their eggs, larvae and pupae to lower and moister galleries.
In these instances, however, we have to deal with thermotropism as well
as hydrotropism.
Thigmotropism. — Negative thigmotropism (stereotropism) as dis-
played in the withdrawal from contact, is a common phenomenon
among animals, from Protozoa to Vertebrata, and is often conducive
304
ENTOMOLOGY
to the safety of an organism; though the negative response occurs
none the less, whether it is to prove useful or not, and occurs as auto-
matically as the collapse of a sensitive plant at a touch.
Positive thigmotropism is less common, though nevertheless wide-
spread among animals. Protozoa and Infusoria cling to solid bodies
and become aggregated about them. Cockroaches squeeze themselves
into crevices until their bodies come into close contact with surrounding
surfaces. A moth, Pyrophila (Amphipyra) pyramidoides, is accustomed
to squeeze into crevices under loose bark or elsewhere, though this habit,
though doubtless protective, is not performed/or the purpose of self-con-
cealment. That this is not a case of negative phototropism, it was
proved by Loeb, who wrote -."Iplaced some of these animals in a box, one-
half of which was covered with a non- transparent body, the other half with
glass. I covered the bottom of the box with small glass plates which
rested on small blocks, and were raised just enough from the bottom to
allow an Amphipyra to get under them. Then the Amphipyra collected
under the little glass plates, where their bodies were in contact with
solid bodies on every side, not in the dark corner where they would
have been concealed from their enemies. They even did this when in so
doing they were exposed to direct sunlight. This reaction also occurred
when the whole box was dark. It was then impossible for anything
but the stereotropic [thigmotropic] stimuli to produce the reaction."
Among the water-striders, Gerridae, thigmotropism is strongly in
evidence at the inception of and during the hibernation period. The
gerrids hibernate in large groups or clusters under dead leaves, in holes
in banks of streams, under logs, etc., with their bodies in close contact
with the substratum. The acts of crawling into and remaining in such
places are evidently due to the contact stimuH that impinge on them at
such times (C. F. C. Riley).
Rheotropism. — Fishes swimming or heading directly against a cur-
rent of water illustrate positive rheotropism. When facing the current,
the resistance of the water is symmetrically distributed on the body of
the animal and is met by symmetrical muscular action, in the most eco-
nomical manner. Many aquatic insects offer such examples of rheo-
tropism, either positive or negative.
E. P. Lyon gives, however, a different explanation. He found that
fishes orient themselves just as well when they are put into a closed
glass bottle, which is dragged through the water, although in this case
they are not under the influence of any friction from the current. When
the bottle is not moved the fishes swim in any direction inside the
INSECT BEHAVIOR 305
bottle. It is obviously the motion of the retina images of the objects
on the bank of the brook which causes the "rheotropic" orientation of
fishes. When driven backward by the current or when dragged back-
ward in a bottle through the water, the objects on the bank of the river
seem to move in the opposite direction. The animal being compelled
to keep the same object fixed, an apparent forward motion of the fixed
object changes the muscles of the fins in such a sense as to cause the
animal to follow the fixed object automatically. When such rheotropic
fishes were kept in an aquarium and a white sheet of paper with black
stripes was moved constantly in front of the aquarium the fishes ori-
ented themselves against the direction in which the paper and its
stripes moved. The phenomenon was more marked in young than in
older specimens. All the phenomena of rheotropism ceased in the dark
or when the fishes were blind. (J. Loeb.)
Anemotropism. — Various flies orient the body with reference to the
direction of the wind. Wheeler observed swarms of the male of Bibio
alhipennis poising in the air, with all the flies headed directly toward the
gentle wind that was blowing. If the wind shifted, the insects at once
changed their position so as again to face to windward; a strong wind,
however, blew them to the ground. The males of an anthomyiid
{Ophyra leucostoma), according to the same naturalist, hover in swarms
in the shade for hours at a time; if the breeze subsides they lose their
definite orientation, but if it is renewed they face the wind with mihtary
precision. In Syrphidae, he finds, either males or females are positively
anemotropic. Midges of the genus Chironomus, which on summer days
dance in swarms for hours over the same spot, orient themselves to
every passing breeze. So also in the case of Empididas, which Wheeler
has observed swarming in one spot every day for no less than two weeks,
possibly on account of "some odor emanating from the soil and attract-
ing and arresting the flies as they emerged from their pupas."
The Rocky Mountain locusts "move with the wind and when the
air-current is feeble are headed away from its source;" when the wind is
strong, however, they turn their heads toward it.
Anemotropism and rheotropism are closely allied phenomena. As
Wheeler says, "The poising fly orients itself to the wind in the same way
as the swimming fish heads upstream," adjusting itself to a gaseous
instead of a liquid current. "In both cases the organism naturally
assumes the position in which the pressure exerted on its surface is sym-
metrically distributed and can be overcome by a perfectly symmetrical
action of the musculature of the right and left halves of the body."
3o6
ENTOMOLOGY
Geotropism.- — Gravity frequently determines the orientation and
direction of locomotion of an animal. A freshly emerged moth hangs
with the abdomen downward and remains in this position until the
wings have expanded. Certain dolichopodid flies found on the bark
of trees "rest or walk with the long axis of the body perpendicular to
the earth and parallel with the long axis of the trunk of the tree and the
head pointing upwards. • When disturbed they fly off, but very soon
alight nearer the earth and again walk upward." (Wheeler.) Cocci-
nellidas (lady beetles) and cockroaches are also negatively geotropic.
The latter insects, as Loeb
has observed, tend to leave
a horizontal surface but
come to rest on a surface
that is vertical or as nearly
so as possible.
Wheeler says, " Geotro-
pic as well as anemotropic
orientation is not altered
for the sake of response to
light. Even if the insect
be strongly heliotropic, as
is the case inmost Diptera,
it orients itself to the wind
or to gravity no matter
whence the light may fall."
Experiments by W. H.
Fig. 296. — yl , tracks made on paper by a larva of Cole shoW that the pomace
Lucilia casar moving out of a spot of ink under the n t-w .7-7 .7
influence of light; a and B show respectively the first AY' i^rOSOpHlla ampelO-
and second directions of the light. jB, tracks made in -hfiHa when creeoinff
the dark.— After Pouchet. r j ^ F a>
reacts negatively to grav-
ity, to a centrifugal force which is equal to or sUghtly greater than
gravity, and to air currents without regard to other stimuli. Gravity
is, then, a kinetic as well as a directive stimulus. The stimuli caus-
ing these reactions are probably received by the sensory nerves of the
leg muscles. (Cole.) .
Phototropism.— It is a matter of common observation that house
flies, butterflies, bees and many other diurnal insects fly toward the
light; and that cockroaches and bedbugs avoid the light. These are
familiar examples of phototropism {heliotropism) or the ''control of the
direction of locomotion by light." The phototropic response is
INSECT BEHAVIOR 307
either positive or negative according as the organism moves, respec-
tively, toward or away from the source of light. Maggots of Lucilia
ccesar and of many other flies are negatively phototropic as a rule (Fig.
296, A), but in the absence of light (other directive stimuH being
excluded, of course) wander about indifferently (Fig. 296, B).
Do the different rays of the spectrum differ in phototropic power?
This question has occurred to many investigators, who have found that,
in general, the rays of shorter wave length, as violet or blue, are more
effective than those of longer wave length, as yellow or red; the latter in
fact acting like darkness. Ants avoid violet rays as they would avoid
direct sunlight, but carry on their operations under yellowish red Hght
as they would in darkness. Miss Fielde has made use of this fact in
studying the habits of ants, by using as a cover for her artificial formi-
caries an orange-red sheet of glass such as the photographer uses for his
dark room. Though ants avoid violet rays, they prefer them to ultra-
violet rays, as Lubbock found.
These responses to light are inevitable on the part of the organism,
whether they are beneficial or harmful, and it is now becoming recog-
nized that the reactions of both plants and animals to light are funda-
mentally the same.
Phototaxis and Photopathy. — A phototropic organism, if bilater-
ally symmetrical, orients itself with the head directly toward or else
directly away from the source of light and moves toward or away from
the light, as the case may be. In either event the long axis of the
organism becomes parallel with the rays of light. Now a ray of light is
ever diminishing in intensity from its source, and it would seem that
differences of intensity along the paths of light rays determine the orien-
tation and consequent direction of locomotion of the organism. Some
investigators, however, distinguish between the effects of intensity of
light and those of its direction. Thus by ingeniously contrived experi-
ments, it has been found, apparently, that Protista (Strasburger),
Daphnia (Davenport and Cannon) and the caterpillars of Porthesia
(Loeb) move toward a source of light even while, in so doing, they are
passing into regions of less intensity of illumination. For this migration
as determined by the direction of the light rays, the term phototaxis is by
some authors (as Davenport) reserved. Usually, however, the
direction of locomotion does depend on differences of intensity, without
regard to the direction whence the light comes. This "migration
towards a region of greater or less intensity of light" has been termed
photopathy, and organisms are said to be photophil or photophob, accord-
308 ENTOMOLOGY
ing as they move, respectively, toward or away from a more intensely
illuminated area.
Verworn and others maintain, however, that differences of intensity
are sufficient to account for all phototropic phenomena.
Optimum Intensity. — It has been found that there is a certain
optimum degree of light, differing according to the organism, toward
which the organism will move, from either a region of greater illumina-
tion or one of less. The organism appears to be attuned to a "certain
range of intensity." This attunement is used by Davenport to explain
apparent anomalies between the response to light of a butterfly and
that of a moth. Butterflies are positively phototropic to sunlight and
most moths are negatively so. Why, then, do moths fly toward a lamp
or an electric light? The answer is given that the moth is positively
phototropic up to a certain intensity of light, at which it becomes nega-
tively phototropic. "Butterflies are attuned to a high intensity of
light,. moths to a low intensity; so that bright sunlight, which calls
forth the one, causes the other to retreat. On the other hand, a light
like that of a candle, so weak as not to stimulate a butterfly, produces a
marked response in the moth." (Davenport.)
The circhng of moths and other insects about a Hght is a matter of
common observation, an explanation for which has been given by Loeb.
Loeb says, "If a moth be struck by the light on one side, those muscles
which turn the head toward the light become more active than those of
the opposite side, and correspondingly the head of the animal is turned
toward the source of light. As soon as the head of the animal has this
orientation and the median-plane (or plane of symmetry) comes into the
direction of the rays of light, the symmetrical points of the surface of the
body are struck by the rays of light at the same angle. The intensity
of light is the same on both sides, and there is no reason why the animal
should turn to the right or left, away from the direction of the rays of
light. Thus it is led to the source of the light. Animals that move
rapidly (like the moth) get into the flame before the heat of the flame has
time to check them in their flight. Animals that move slowly are
affected by the increasing heat as they approach the flame; the high
temperature checks their progressive movement and they walk or fly
slowly about the flame." As Loeb insists, the moth "does not fly into
the flame out of 'curiosity,' neither is it 'attracted' by the light; it is
only oriented by it and in such a manner that its median-plane is
brought into the direction of the rays and its head directed toward the
INSECT BEHAVIOR 309
source of light. In consequence of this orientation its progressive
movements must lead it to the source of light."
Factors Influencing Phototropism. — The response of an organism
to light is influenced by previous exposure to light, by temperature,
moisture, nutrition and other factors, all of which have to be taken into
account in experiments on phototropism.
Loeb found that larvae of the brown-tail moth, Euproctis chrysor-
rhcea, driven by the warm sunshine out of the nest in which they have
hibernated, crawl upward to the tips of branches and feed upon the
buds and new leaves. This self-preservative "instinct" is purely a
response to light. The caterpillars are positively phototropic, and as
the horizontal components of the surrounding light neutralize each
other, only the light from above is effective as a stimulus to orientation.
After feeding, however, the larvae are no longer positively phototropic
and crawl downward; in other words, they are positively phototropic
only so long as they are unfed. Here the kind of phototropism is
dependent upon nutrition.
Phototropism may be overruled by chemotropism and influenced by
conditions of metabolism, as Parker found for the butterfly Vanessa
antiopa. In his words: Vanessa antiopa, in bright sunlight, comes to
rest with the head away from the source of light, that is, it is negatively
phototropic, when the surface on which it settles is not perpendicular
or very nearly perpendicular to the direction of the sun's rays. When,
however, this surface is'perpendicular to the sun's rays the insect settles
without reference to the direction of the rays. When feeding or near
food [such as running sap] the butterflies do not respond phototropically.
This negative phototropism is seen only in intense sunlight and after
the butterfly has been on the wing, i.e., after a certain state of metab-
olism has been established.
V. antiopa creeps and flies toward a source of light, that is, it is
positively phototropic in its locomotor responses. Positive photo-
tropism also occurs in intense sunKght, and is not dependent upon any
particular phase of metabolism.
Both negative and positive phototropism in this species are inde-
pendent of the "heat rays" of sunlight.
The position assumed in negative phototropism exposes the color
patterns of the wings to fullest illumination, and probably has to do
with bringing the sexes together during the breeding season.
To these may be added other important conclusions of Parker's;
3IO ENTOMOLOGY
No light reactions are obtained from the butterfly when shadows are
thrown upon any part of the body except the head. When one eye is
painted black the butterfly creeps or flies in circles ("circus move-
ments") with the unaffected eye always toward the center. When both
eyes are painted black all phototropic responses cease and the insect fldes
upward. Butterflies with normal eyes liberated in a perfectly dark room
come to rest near the ceiling. _ This upward flight in both cases is due
to negative geotropism, not to phototropic activity.
V. antiopa does not discriminate between lights of greater or less
intensity provided they are all of at least moderate intensity and of
approximately equal size. V. antiopa does discriminate between light
derived from a large luminous area and that from a small one, even when
the hght from these two sources is of equal intensity as it falls on the
animal. These butterflies usually fly toward the larger areas of light.
This species remains in flight near the ground because it reacts positively
to large patches of bright sunlight rather than to small ones, even
though the latter, as in the case of the sun, may be much more
intense.
V. antiopa retreats at night and emerges in the morning, not
so much because of light differences, as because of temperature
changes. On warm days it will, however, become quiet or active,
without retreating, depending upon a sudden decrease or increase of light.
The maggots of the muscid Phormia regina are, as the author has
observed, negatively phototropic until full grown, when they become
positively phototropic for an hour or less, leave the decaying matter in
which they have developed and wriggle along the ground toward the
sun; or if the sunhght is diffused by clouds, wander about aimlessly,
but at length bury themselves in the ground to pupate. Here the
positive phototropism just before pupation is adaptive.
The swarming of the honey bee is likewise a case of periodic positive
phototropism, as Kellogg has observed.
Winged ants of both sexes are strongly positively phototropic when
they swarm from the ground for the nuptial flight. After mating,
however, the female becomes negatively phototropic and positively
thigmo tropic; enters the ground, sheds her wings, and enters upon a
subterranean existence, during which she is intensely positively thigmo-
tropic. In connection with this subject, it is a significant fact that the
pomace fly, Drosophila, loses its phototropism when its wings are
removed artificially.
In autumn, gravid females of the mosquito, Culex pipiens, become
INSECT BEHAVIOR
Strongly negatively phototropic and seek dark hibernation quarters, in
spite of warm temperatures that may prevail. If hibernating in a
warm place the mosquito becomes positively thigmotropic, and loses
its phototropism, prolonged exposure to strong lights producing no
response, though the insect responds actively to mechanical stimuli. It
is also negatively geotropic, as it always assumes a position with the
long axis of the body perpendicular to the earth and the head pointing
upward. (H. B. Weiss.)
Though adaptive in their results, these phototropic reactions can
scarcely be said to be performed on account of their usefulness. They
are performed anyway, and may result harmfully, as when they lead
a moth into a flame or, to take a more natural example, when they
expose an insect to its enemies.
Phototropism and thermotropism, either together or singly, as
Wheeler suggests, may explain the up and down migration of insects in
vegetation. "On cold, cloudy days few insects are taken because they
lurk quietly near the surface of the soil and about the roots of the vegeta-
tion, but with an increase in warmth and Hght they move upwards
along the stems and leaves of the plants, and, if the day be warm and
sunny, escape into the air."
F. Payne bred sixty-nine successive generations of the pomace fly,
Drosophila ampelophila in the dark without any resultant effect upon
either the eyes or the phototropism of the flies.
Drosophila is usually positively phototropic, but R. S. McEwen
obtained a mutant which is not phototropic; this character being
"linked" with a characteristic "tan" color.
Muscle Tension Theory. — Experiments by Professor S. J. Holmes
with water scorpions (Ranatra) showed that when the insect is illuminated
from the right side the legs on the right side are flexed and those of the left
side are extended, with a resultant locomotion toward the light. These
and other experiments "leave no doubt that the primary effects of light
consist in changes in the tension of muscles." (Loeb.) The muscle tone
is dependent upon the intensity of the light. If a positively phototropic
insect is illuminated from one side only it turns toward the light until the
muscle tension is equal on the two sides of the body; then locomotion is
inevitably toward the source of light. The stimulus is received through
the eyes.
Artificial Heliotropic Machine.— As illustrating the purely
mechanical nature of the response to light, the artificial heliotropic
machine, as described by Loeb, may be referred to. Briefly, this
312 ENTOMOLOGY
electrically-operated machine, invented by Mr. John Hays Hammond,
Jr., is a box containing the mechanism and mounted on three wheels.
Two of these are geared to a driving motor and the third, on the rear
end, can be turned by means of electro-magnets in a horizontal plane.
A pair of five-inch condensing lenses on the front end look hke large
eyes. If a portable electric Hght, as a hand flashhght, be turned on
in front of the machine this will immediately move toward the light and
will follow the light all around the room in complex manoeuvers at a
speed of about three feet per second. Upon shading or switching
off the light the "dog," as it is called, can be stopped at once, but will
resume its uncanny movements as soon as the light reaches the "eyes"
of the machine in sufficient intensity. The orientation mechanism
possesses two selenium cells, one behind each "eye," which when influ-
enced by light effect the control of sensitive relays, analogous to the nerv-
ous system of a moth. These relays operate electro-magnetic switches,
which control the driving motors and the steering wheel.
The principle of this mechanism has been applied to the "Hammond
dirigible torpedo."
Thermotropism. — Ants are strongly thermotropic; they carry their
eggs, larvae and pupae from a cooler to a warmer place or vice versa,
and thus secure optimum conditions of temperature. Caterpillars and
cockroaches migrate to regions of optimum temperature.
In thermotropism it appears that the direction of heat rays has
little or no effect as compared with differences of intensity.
Tropisms in General. — Other kinds of tropisms are known, for
example, tonotropism, or the control of the direction of locomotion
by density, and electrotropism {galvanotropism) ; not to mention any
more.
All these phenomena are responses of protoplasm to definite stimuli
and are almost as inevitable as the response of a needle to a magnet.
The tropisms of the lower organisms have been experimented upon
by many skilled investigators, whose results furnish a broad basis for
the study of the subject in the higher animals. Even in the simplest
organisms, behavior is the resultant effect of several or many stimuli
acting at once, and the precise effect of each stimulus can be ascertained
only by the most guarded kind of experimentation; while in the higher
animals, with their complex organization, including speciahzed sense
organs, the study of behavior becomes intricate and cannot be carried
on intelligently without an extensive knowledge of the behavior of uni-
cellular organisms. The properties of protoplasm are the key to the
INSECT BEHAVIOR 313
behavior of organisms. Furthermore, the study of tropic reactions is
complicated by the fact that they are due not only to external stimuli,
but also to Httle-understood internal stimuli, arising from unknown
conditions of the alimentary canal, muscles, reproductive organs, etc.
A recognized property of protoplasm is that of adaptation, as mani-
fested in the acclimatization of protoplasm to untoward conditions
of temperature, hght, contact and other stimuH; and this adaptation to
unusual conditions may take place without the aid of natural selection.
A tropic reaction occurs, whether it is to prove useful to the organism
or not. Thus a lady-bird beetle walks upward, on a branch, on a fence,
on one's finger. It walks upward as far as possible and then flies into
the air. If it happens to reach the tip of a twig and finds aphids there,
the beetle stops and feeds upon them. This adaptive result is in a sense
incidental. Yet, upon the whole, tropic reactions are wonderfully adap-
tive in their results. Here natural selection is of special value as afford-
ing an explanation of the phenomena.
As Loeb and Davenport have insisted, the mechanical reactions to
gravity, light, heat and other influences determine the behavior of the
organism.
2. Instinct
Insects are eminently instinctive; though their automatic behavior
is often so remarkably successful as to appear rational, instead of purely
instinctive.
A satisfactory definition of "instinct" seems to be impossible,
though some of the characteristics of instinctive behavior are quite
evident.
Instinct, as distinguished from reason, attains adaptive ends without
prevision and without experience. For example, a butterfly selects a
particular species of plant upon which to lay her eggs. Caterpillars of
the same species construct the same kind of nest, though so isolated from
one another as to exclude the possibility of imitation. Every caterpillar
that pupates accomplishes the intricate process after the manner of its
kind, without the aid of experience.
Instinctive actions belong to the reflex type — they consist of co-or-
dinated reflex acts. A complex instinctive action is a chain, each link
of which is a simple reflex act. In fact, no sharp line can be drawn
between reflexive and instinctive actions.
Basis of Instinct.— Reflex acts, the elements from which instinctive
actions are compounded, are the inevitable responses of particular organs
314 ENTOMOLOGY
to appropriate stimuli, and involve no volition. The presence of an
organ normally implies the ability to use it. The newly born butterfly
needs no practice preliminary to flight. The process of stinging is
entirely reflex; a decapitated wasp retains the power to sting, directing its
weapon toward any part of the body that is irritated; and a freshly
emerged wasp, without any practice, performs the stinging movements
with greatest precision.
As Whitman observes, the roots of instincts are to be sought in the
constitutional activities of protoplasm.
Apparent Rationality. — The ostensible rationality of behavior
among insects, as was said, often leads one to attribute intelligence to
them, even when there is no evidence of its existence. As an illustra-
tion, many plant-eating beetles, when disturbed, habitually drop to the
ground and may escape detection by remaining immovable. We
cannot, however, believe that these insects "feign death" with any con-
sciousness of the benefit thus to be derived. This act, widespread
among animals in general, is instinctive, or reflex, as Whitman maintains,
being at the same time, one of the simplest, most advantageous and
deeply seated of all instinctive performances.
Take the many cases in which an insect lays her eggs upon only one
species of plant. The philenor butterfly hunts out Aristolochia, which
she cannot taste, in order to serve larvae, of whose existence she can have
no foreknowledge. Oviposition is here an instinctive act, really a
chemotropism, which is not performed until it is evoked by some sort
of stimulus — probably an olfactory one — from a particular kind of plant.
Stimuli. — Some determinate sensory stimulus is, indeed, the neces-
sary incentive to any reflex act. The first movements of a larva within
the egg-shell are doubtless due to a sensation, probably one of tem-
perature. Simple contact with the egg-shell is probably sufficient to
stimulate the jaws to work, and the caterpillar eats its way out; yet it
cannot foresee that its biting is to result in its liberation. Nor, later on,
when voraciously devouring leaves, can the caterpillar be supposed to
know that it is storing up a reserve supply of food for the distant period
of pupation and the subsequent imaginal stage. The ends of these
reflex actions are proximate and not ultimate, except from the stand-
point of higher intelhgence.
Just as simple reflexes link together to form an instinctive action, so
may instincts themselves combine. The complex behavior of a solitary
wasp is a chain of instincts, as the Peckhams have shown. All the opera-
tions of making the nest, stinging the prey, carrying it to the nest, etc..
INSECT BEHAVIOR 315
are performed as a rule in a definite, predicable sequence, and even a
slight interference with the normal sequence disconcerts the insect.
Just as the performance of one reflex act may serve as the stimulus for
the next reflex in order, so the completion of one instinctive action may
be in part the stimulus for the next one.
Modification of Instincts. — An action can be regarded as purely
instinctive in its initial performance only, because every subsequent
performance may have been modified by experience; in other words,
habits may have been forming and fixing, so that the results of instinct
become blended with those of experience. Thus the first flight of a
dragon fly is instinctive and erratic, but later efforts, aided by experience,
are well under control.
When once shaped by experience, reflex or instinctive actions tend
to become intense habits. Thus, certain caterpillars, having eaten all
the available leaves of a special kind, will almost invariably die rather
than adopt a new food plant, whereas larvae of the same species will eat-
a strange plant if it is offered to them at birth. An act is strengthened
in each repetition by the influence of habit, to the increasing exclusion
of other possible modes of action. Many a caterpillar, having eaten its
way out of the egg-shell, does not stop eating, but consumes the remain-
der of the shell — a reflex act, started by a stimulus of contact against the
jaws and continued until the cessation of the stimulus, unless some
stronger stimulus should intervene. It has been said that the larva eats
the remains of the shell because they might betray its presence to its
enemies. Whether this is true or not, to assume conscious foresight of
such a result on the part of an inexperienced caterpillar is worse than
unnecessary.
With insects, as with other animals, many instincts are transitory;
even when partially fixed by habit, they are replaceable by stronger
instincts. Thus the gregarious habit of larvae is finally overpowered by
a propensity to wander, which does not mature, however, until the
approach of the transformation period. The reproductive instinct is
another of those impulses that do not ripen until a certain age in the
individual.
Inflexibility of Instincts. — Broadly speaking, instinctive actions
lack individuality — are performed in the same way by every individual
of the species. The solitary wasps of the same species are remarkably
consistent in architecture, in the selection of a special kind of prey, in
the way they sting it, carry it to the nest and dispose of it; all these
operations, moreover, are performed in a sequence that is characteristic
3l6 ENTOMOLOGY
of the species. Examples of this so-called inflexibility of instinct are
so omnipresent, indeed, that insect behavior as a whole is admitted to
be instinctive, or automatic. Insects are capable of an immense num-
ber of reflex impulses, ready to act singly or in intricate correlation,
upon the requisite stimuli from the environment.
To normal conditions of the environment, the behavior of an insect
is accurately adjusted; but in the face of abnormal circumstances
demanding the exercise of judgment, most insects are helpless. The
speciahzation to one kind of food, though usually advantageous, is fatal
if the supply becomes insufiicient and the larva is unable to adopt
another f ood . A species of Sphex habitually drags its grasshopper victim
by one antenna. Fabre cut off both antennae and then found that the
wasp, after vain efforts to secure its customary hold, abandoned the
prey. Under such unaccustomed conditions, insects often show a sur-
prising stupidity, capable as they are amid ordinary circumstances.
Flexibility of Instincts. — Notwithstanding such examples, the
common assertion that instincts are absolutely "blind," or inflexible, is
incorrect. Instinctive acts are not mechanically invariable, though
their variations are so inconspicuous as frequently to escape casual
observation. A precise observer can detect individual variations in the
performance of any instinctive act — variations analogous to those of
structure.
To take extreme examples, the Peckhams found that an occasional
queen of Polistes fusca would occupy a comb of the previous year,
instead of building a new one ; and that an individual of Pompilus mar-
ginatus, instead of hiding her captured spider in a hole or under a lump
of earth as usual, hung it up in the fork of a purslane plant. They
observed also that one Ammophila, in order to pound down the earth
over her nest, actually used a stone, held between the mandibles (Fig.
297).
This performance, which has been witnessed also by Professor
Williston and a few other observers, illustrates the flexibihty of in-
stinctive action, and has been cited as an instance of adaptability, or
intelligence. It can not be supposed, however, that the insect is
conscious of the efficiency of a stone as a tool. The performance may be
an accident. If one observes an Ammophila at work he will notice that
she not only pounds down the earth with her head, but also lifts and
lays aside small stones with her mandibles. Possibly she now and then
chances to begin the pounding movement before she has happened to
release a stone from her jaws.
INSECT BEHAVIOR 317
Even the despotic power of habit may be overborne by individual
adaptability. Among caterpillars that have exhausted their customary
food, there are often a few that will adopt a new food plant and survive,
leaving their more conservative fellows to starve.
As Darwin himself held, the doctrine of natural selection is applicable
to instincts as well as structures. All reflex acts are to some extent
variable. Disadvantageous reflexes or combinations of reflexes elimi-
nate themselves, while advantageous ones persist and accumulate.
Indeed, structures and instincts must frequently have evolved hand
in hand. The remarkable protective resemblance of the Kallima butter-
FiG. 297. — Ammophila urnaria using a stone to pound down the earth over her nest.
Greatly enlarged. — After Peckham, from Bull. Wisconsin Geol. and Nat. Hist. Survey.
fly would be useless, did not the insect instinctively rest among dead
leaves of the appropriate kind.
Origin of Instinct. — There are two leading theories as to the origin
of instinct. Lamarck, Romanes and their followers have regarded in-
stinct as inherited habit; have supposed that instincts have originated
by the relegation to the reflex type of actions that at first were rational,
and that instincts represent the accumulated results of ancestral experi-
ence. This habit theory, however, has little to support it, and assumes
the inheritance of acquired characters — which has not been proved.
The selection theory of Darwin, Weismann, Morgan and others has
much in its favor. It regards reflex acts as primitive, as the raw
material from which natural selection, as the chief factor, has effected
those combinations that are termed instincts.
3l8 ENTOMOLOGY
Instincts and Tropisms. — We have already emphasized the fact
that an instinct is a reflex act or a combination of reflex acts. The same
fact may now be stated in these words: an instinct is a tropism or a
combination of tropisms. The more important of these tropisms have
been considered. Whenever possible it is better to discard the ambigu-
ous term instinct in favor of such more precise terms as phototropism,
geotropism, etc.; though the term instinct remains useful as applied to an
action that is the resultant of several tropic responses.
The modern student of instincts aims to resolve them into their
component reflexes and to determine as precisely as possible the influ-
ence of each reflex component. Thanks to the labors of a great number
of skilled investigators, we are no longer satisfied to class an action as
"instinctive" and then dismiss it from thought; for we are now in a
position to analyze the action, and may hope to explain it eventually
in terms of the physical and chemical properties of protoplasm.
3. Intelligence
Though manifestly dominant, pure instinct fails to account for all
insect behavior. The abihty of an insect to profit by experience indi-
cates some degree of intelligence.
Take, for example, the precision with which bees or wasps find their
way back to the nest. This is no longer to be accounted for on the as-
sumption of a mysterious "sense of direction," for there is the best of
evidence for believing that it depends upon the recognition of surround-
ing objects. When leaving the nest for the first time, these insects make
"locality studies," which are often elaborate. Referring to a digger-
wasp, Sphex ichneumonea, the Peckhams write: "At last, the nest dug,
she was ready to go out and seek for her store of provision and now came
a most thorough and systematic study of the surroundings. The nests
that had been made and then deserted had been left without any
circling. Evidently she was conscious of the difference and meant,
now, to take all necessary precautions against losing her way. She
flew in and out among the plants first in narrow circles near the surface
of the ground, and now in wider and wider ones as she rose higher in the
air, until at last she took a straight line and disappeared in the distance.
The diagram [Fig. 298, A] gives a tracing of her first study preparatory
to departure. Very often after one thorough study of the topography
of her home has been made, a wasp goes away a second time with much
less circling or with none at all. The second diagram [Fig. 298, B] gives
a fair illustration of one of these more hasty departures. ,
INSECT BEHAVIOR
319
"If the examination of the objects about the nest makes no impres-
sion upon the wasp, or if it is not remembered, she ought not to be
inconvenienced nor thrown of! her track when weeds and stones are
removed and the surface of the ground is smoothed over; but this is
just what happens. Aporus fasciatus entirely lost her way when we
broke off the leaf that covered her nest, but found it without trouble
when the missing object was replaced. All the species of Cerceris were
extremely annoyed if we placed any new object near their nesting-places.
Our Ammophila refused to make use of her burrow after we had drawn
Fig. 298. — Locality studies made by a wasp, Sphex ichneumonea. A, a thorough study;
B, a hasty study; «, nest. — After Peckham, from Bull. Wisconsin Geol. and Nat. Hist.
Survey.
some deep Hnes in the dust before it. The same annoyance is exhibited
when there is any change made near the spot upon which the prey of
the wasp, whatever it may be, is deposited temporarily."
If we take, as one criterion of inteUigence, the power to choose be-
tween alternatives, then insects are more inteUigent than is generally
admitted. The control of locomotion, the selection of prey, and the
avoidance of enemies, as results of experience, indicate powers of dis-
crimination. The power of intercommunication, conceded to exist
among social Hymenoptera, implies some degree of intelligence.
If instinct is bhnd, or mechanical, with no adjustment of means to
ends, then a pronounced individuality of action must signify something
more than instinct. In regard to a female Pompilus scelestus, which had
dragged a large spider nearly to her nest, the Peckhams observe:
320
ENTOMOLOGY
"presently she went to look at her nest and seemed to be struck with a
thought that had already occurred to us — that it was decidedly too
small to hold the spider. Back she went for another survey of her
bulky victim, measured it with her eye, without touching it, drew her
conclusions, and at once returned to the nest and began to make it larger.
We have several times seen wasps enlarge their holes when a trial had
demonstrated that the spider would not go in, but this seemed a remark-
ably intelligent use of the comparative faculty."
From the standpoint of pure instinct, indeed, much of the behavior
of the solitary wasps is inexplicable; while the actions of the social
Hymenoptera have led some of the most critical students to ascribe
intelligence to these insects. The activities of the harvesting ants, the
miHtary or the slave-holding species, are of such a nature that the
possibility of education by experience and instruction is strong, to say
the least. In fact, Forel has maintained that a young ant is actually
trained to its domestic duties by its older companions.
In his scholarly volume, Ants, Wheeler shows that these insects
have the ability tcr profit by experience, as exhibited in their foraging
and homing operations, the recollection of nest-mates and aliens,
communication, imitation and co-operation; and that they have
memory in the general sense of the word, but that they have memory
images only as the result of sensory stimulation, and are unable to call
them up at will, much less to refer them to the absent or to the past.
"If this moderate estimate of the memory of ants be correct, it follows
that they must be incapable of reasoning — of 'focusing the wherefore,'
to use Lloyd Morgan's expression, for a mere association of sense impres-
sions is not deducing conclusions from premises." (Wheeler.)
It is extremely difl&cult, if not impossible, however, to draw the line
between instinct and intelUgence; and in doubtful cases there is a gen-
eral tendency to exaggerate the importance of intelligence rather than
that of instinct. For example, the well-known discrimination on the part
of ants between members of their own colony and those of other colonies,
even of the same species, would seem to imply intelligent recognition.
This recognition is due, however, to a characteristic odor, which
is derived from the mother of the community. An ant after being washed
receives hostile treatment from others in its own colony; while an alien
ant after being smeared with the juices of hostile ants is treated by the
latter as a friend.
Each instance of apparent intelligence must be examined impartially
on its own merits. At present it may be said that, while most of the
INSECT BEHAVIOR 32I
behavior of insects is purely instinctive, there is some reason to believe
that at least gleams of intelligence appear in the most speciahzed
Hymenoptera.
Lack of Rationality.- — However intelligent the social Hymenoptera
may be in their way, they show no signs of the power of abstract reasoning.
Even ants, according to the experiments of Lubbock, display profound
stupidity in the face of novel emergencies from which they might
extricate themselves by abstract reasoning of the simplest kind. The
thoughts of an ant or bee seem to be limited to simple associations of
concrete things. Miss Enteman observed a Polistes worker which
gnawed a piece out of the side of a dead larva of its own kind and, turn-
ing, actually offered it as food to the mouth of the same larva. In
another instance a larva was attacked and killed, and then offered a
piece of its own body.
Such examples as these emphasize the strength of the reflex factor in
the behavior of insects. Indeed, the basis of all behavior is being sought
in the reactions of protoplasm to external stimuli. Possibly even mem-
ory, consciousness and other attributes of intelhgence will eventually be
reduced to this basis, improbable as it may now seem. •
CHAPTER XII
DISTRIBUTION
I. Geographical
Importance of Dispersion. — Dispersion enables species to miti-
gate the intense competition and the rigid selection that result from
crowded numbers; hence the tendency to disperse, being self -preserva-
tive, has become universal. Some species habitually emigrate in pro-
digious numbers: the African migratory locust, the Rocky Mountain
locust, and the milkweed butterfly, which annually leaves the Northern
states for the South in immense swarms, in autumn, and in the follow-
ing spring straggles back to the North. Vanessa cardui occasionally
migrates in immense numbers, as do also Fieri s, some dragon flies and
some beetles, notably CoccinelHdae.
Wide Distribution of Insects. — Insects have been found in almost
every latitude and altitude explored by man. Butterflies and mos-
quitoes occur beyond the polar circle, the former in Lat. 83° N., the
latter in Lat. 72° N., and a species of Emesa closely aUied to our common
E. longipes is recorded by Whymper from an altitude of 16,500 ft. in
Ecuador, where, according to the same traveler, Orthoptera occur at
16.000 ft., Pieris xanthodice ranges above 15,000 ft., and dragon flies,
Hymenoptera and scorpions reach a height of 12,000 ft., while twenty-
nine species of Lepidoptera range upward of 7,300 ft. A very few
species of insects inhabit salt water, Halobates being found far at sea;
some kinds live in arid regions and a few even in hot springs, while
caves furnish many pecuhar species. In short, insects are the most
widely distributed of all animals, excepting Protozoa and possibly
Mollusca.
While all the large orders of insects are world-wide in distribution,
the most richly distributed are Coleoptera, Thysanura and Collembola,
the last two feeding usually upon minute particles of organic matter in
the soil and being remarkably tolerant of extremes of temperature.
The four chief families of butterflies occur the world over, as do several
families of beetles. Of species that are essentially cosmopoHtan we may
mention the coWemholsm Folsofnia fimetaria, and the butterflies Vanessa
cardui and Anosia plexippus, while among beetles no less than one hun-
322
DISTRIBUTION 323
dred species are cosmopolitan or subcosmopolitan, including Tenehrio
molitor, Silvanus surinamensis, Dermestes lardarius, Attagenus piceus
and Calandra oryza. The coccinellid genus Scymnus occurs in North
America, Europe, Hawaii, Galapagos Islands and New Zealand, and
Anohium and Hydrobius are distributed as widely. The huge noctuid,
Erebus odora, occurring in Brazil on the lowlands, and in Ecuador at an
altitude of 10,000 ft., finds its way up into the United States and even
into Canada. The chinch bug and many other Central American forms
also spread far northward, as described beyond.
Means of Dispersal. — This exceptional range of insects is due to
their exceptional natural advantages for dispersal, chief among which
are the power of flight and the ability to be carried by the wind. The
migratory locust, Schistocerca peregrina, has been found on the wing five
hundred miles east of South America. The home of the genus, accord-
ing to Scudder, is Mexico and Central America, where 23 species are
found; 20 occurring in South America, including the Galapagos Islands,
II in the United States and 6 in the West Indies; and there is every
reason to believe that S. peregrina — the biblical locust and the only
representative of its genus in Africa — crossed over from South America,
where it is found indeed at present. Darwin and others have recorded
many instances of insects being taken alive far at sea; Trimen mentions
moths and longicorn beetles as occurring 230 miles west of the African
coast and Sphinx convolvulus as flying aboard ship 420 miles out. In
these instances the insects have usually been assisted or carried by
strong winds, particularly the trade-winds, and oceanic islands have
undoubtedly been colonized in this way. On land, Webster has found
that the direction in which the Hessian fly spreads is determined largely
by the prevailing winds at the time when these delicate insects are on
the wing, and that the San Jose scale insect spreads far more rapidly
with the prevailing winds than against them, the wind carrying the
larvae as if they were so many particles of dust. The pernicious buffalo-
gnat of the South emerges from the waters of the bayous and may be
carried on a strong wind to appear suddenly in enormous numbers
twenty miles distant from its breeding place. Mosquitoes are dis-
tributed locally by Hght breezes, but chng to the herbage during strong
winds.
Ocean currents may carry eggs, larvae or adults on vegetable drift
to new places thousands of miles away. Thus the Gulf Stream annually
transports thousands of tropical insects to the shores of Great Britain,
where they do not survive, however.
324 ENTOMOLOGY
Fresh-water streams convey incalculable numbers of insects in all
stages; and insects as a whole are very tenacious of life, being able to
withstand prolonged immersion in water, and even freezing, in many
instances, while they can hve for a long time without food.
The universal process, of soil-denudation must aid the diffusion of
insects, slowly but constantly.
Birds and mammals disseminate various insects in one way or
another, while the agency of man is, of course, highly important. In-
tentionally, he has spread such useful species as the honey bee, the silk-
worm and certain useful parasites; incidentally he has distributed the
San Jose scale, Colorado potato beetle, gipsy moth and many other
pests.
Barriers. — The most important of the mechanical barriers which
limit the spread of terrestrial species is evidently the sea. Mountain
ranges retard distribution more or less successfully, though a species
may spread along one side of a range and sooner or later pass through a
break or else around one end. Mountain chains act as barriers,
however, chiefly because they present unendurable conditions of
climate and vegetation. For the same reason deserts are highly effect-
ive barriers. Indeed the most important checks upon distribution are
those of climate, and of cUmatal factors temperature is the most power-
ful. Tropical species cannot, as a rule, survive and reproduce in
regions of frost; most of the tropical species which have entered the
United States are restricted to its narrow tropical belts (Plate IV).
The stages of an insect are frequently so accurately adjusted to par-
ticular climatal conditions that an unfamiliar climate deranges the life
cycle. Thus many Southern butterflies find their way every year to
the Northern states, only to perish without reproducing their kind.
Insects are, nevertheless, more adaptable than most other animals in
respect to climate, and frequently follow their food plants into new
climates, as in the case of the harlequin cabbage bug, which has pushed
north from the tropics to Missouri, southern Ilhnois and Indiana.
Humidity ranks next to temperature in the importance of its
influence upon the distribution of organisms, but in the case of animals
acts for the most part indirectly, by its effects upon vegetation. Thus
the effectiveness of an arid region as a barrier is due chiefly to the lack of
vegetation in consequence of the lack of moisture. Excessive moisture,
on the other hand, may act as a barrier. The Rocky Mountain locust,
which formerly migrated eastward in immense swarms, succumbed in the
moist valley of the Mississippi; the chinch bug is never seriously injur-
DISTRIBUTION 325
ous in wet years. Moisture checks the development of these and other
insects in ways as yet unascertained; possibly it acts indirectly by favor-
ing the growth of fungus diseases, to which insects are much subject.
The absence of proper food is more effective than climate, as a direct
check upon the spread of an animal; food itself being, of course, de-
pendent ultimately upon climatal factors and soil. Many insects, being
confined to a single food plant, can not exist long where this plant does
not occur ; but they will follow the plant, as was just said, into new
climates; thus Anosia plexippus is following the milkweed over the
world. The butterfly Euphydryas phaeton is remarkably local in its
occurrence, being limited to swamps where its chief food plant {Chelone
glabra) grows ; and Epidemia epixanthe is similarly restricted to cranberry
bogs.
Former Highways of Distribution. — Many facts of distribution
which are inexplicable under the present conditions of topography and
climate become intelHgible in the Hght of geological history. The
marked similarity between the fauna of Europe and that of North
America means community of origin; and though the Arctic zone now
interposes as a barrier, there was once an opportunity for free dispersion
when, in the early Pleistocene or late Pliocene, a land connection existed
between Asia and North America and a warm climate prevailed
throughout what is now the Arctic region.
The extraordinary isolation of the butterfly CEneis semidea on moun-
tain summits in New Hampshire and Colorado (particularly Mt.
Washington, N. H., and Pikes Peak, Col.) is explained by glacial geology.
The ancestors of this species, it is thought, were driven southward be-
fore an advancing ice-sheet and then foflowed it back as it retreated
northward, adapted as they were to a rigorously cold cKmate. Some
of those ancestors presumably followed the melting ice up the mountain
sides, until they found themselves stranded on the summits. Other
individuals, undiverted from the lowlands, followed the retreating glacier
into the far north; and at present there occurs throughout Labrador a
species of CEneis which differs but sHghtly from its lonely ally of the
mountain tops.
Glaciation undoubtedly had a profound effect upon the fauna and
flora of North America. "With the slow southward advance of the ice,
animals were crowded southward; with its recession they advanced
again northward to reoccupy the desolated region, until now it has long
been repopulated, either with the direct descendants of its former in-
habitants or with such limitations to the integrity of the fauna as this
326 ENTOMOLOGY
interruption of local life may have caused." (Scudder.) Probably
many species were exterminated and many others became greatly modi-
fied, though little is known as to the relationship of the present fauna to
the preglacial fauna. "The glacial cold still lingers over the northern
part of this continent and our present animals are only a remnant of
the rich fauna that existed in former ages, when the magnolia and the
sassafras thrived in Greenland."
Island Faunae. — The abihty of insects to surmount barriers, under
favorable circumstances, is strikingly shown in the colonization of
oceanic islands. Not a few insects, including Vanessa cardui, have
found their way to the isolated island of St. Helena. In the Madeira
Islands, according to Wollaston, there are 580 species of Coleoptera, of
which 314 are known to occur in Europe, while all the rest are closely
allied to European forms. Subtracting 120 species as having been intro-
duced probably or possibly through the agency of man, there remain
194 that have been introduced by "natural" means. The rest, 266
species, are endemic, though akin to European species.
The scanty insect fauna of the Galapagos Islands includes twenty
species of Orthoptera, which have been studied by Scudder and by Snod-
grass. Five of these are cosmopolitan cockroaches, doubtless intro-
duced commercially, and the remaining fifteen are all "distinctly South
and Central American in their affinities." Three of these fifteen are
strong-winged species which doubtless arrived by flight from the neigh-
boring mainland; indeed, Scudder records a Schistocerca {S. exsul) as
having been taken at sea two hundred miles off the west coast of South
America, or nearly half way to the Galapagos Islands. Thirteen of the
fifteen are endemic, and five are apterous or subapterous, while a sixth
has an apterous female. Apterous insects, noticeably common on
wind-swept oceanic islands, may have been carried thither on drift-
wood, though it is more likely that the apterous condition arose on the
islands, where the better-winged and more venturesome individuals may
.have been constantly swept out to sea and drowned, leaving the more
feeble-winged and less venturesome individuals behind, to reproduce
their own life-saving peculiarities.
The Coleoptera of the Hawaiian Islands, studied by Dr. Sharp, num-
ber 428 species, representing 38 famihes, and "are mostly small or very
minute insects," the few large forms being non-endemic, with little or
no doubt; 352 species are at present known only from this archipelago.
Dr. Sharp distinguishes three elements in the fauna: "first, species that
have been introduced, in all probabiUty comparatively recently, by arti-
DISTRIBUTION 327
ficial means, such as with provisions, stores, building timber, ballast, or
growing plants; many of these species are nearly cosmopolitan. Second,
species that have arrived in the islands, and have become more or less
completely naturalized; they are most of them known to be wood- or
bark-beetles, but some that are not so may have come with the earth
adhering to the roots of floating trees; a few, such as the Dytiscidae, or
water beetles, may possibly have been introduced by. violent winds.
Third, after making every allowance for introduction by these artificial
and natural methods, there still remains a large portion standing out
in striking contrast with the others, which we are justified in considering
strictly endemic or autochthonous." Among the introduced genera are
Coccinella, Dermestes, Aphodius, Buprestis, Ptinus and Ceramhyx. The
immigrant longicorns appear to have been derived "from the nearest
lands in various directions" — the Phihppine Islands, tropical America
and the Polynesian Islands — and the same conclusion will probably be
found to hold for the other immigrants, when their general distribution
shall have been suj6&ciently studied. The endemic species number 214,
or exactly half the total number of species, and are distributed among 9
families, as follows:
Families. Species. Genera. Endemic
Genera.
Carabidae 51 7 7
Staphylinidae 19 3 i
Nitidulidae 38 2 i
Elateridae 7 i i
Ptinidas (Anobiini) 19 3 3
Cioidae 19 i o
Aglycj'deridse 30 i i
Curculionidae (Cossonini) 21 3 3
Cerambjxidae 10 i i
Sharp writes: "I think it may be looked on as certain that these
islands are the home of a large number of peculiar species not at present
existing elsewhere, and if so it follows that either they must have existed
formerly elsewhere and migrated to the islands, and since have become
extinct in their original homes, or that they must have been produced
within the islands. This last seems the simpler and more probable sup-
position, and it appears highly probable that there has been a large
amount of endemic evolution within the limits of these isolated islands."
The parasitic Hymenoptera of Hawaii, according to Ashmead, num-
ber 14 families, 69 genera and 128 species; only eleven genera are en-
demic and most of the other genera are represented in nearly all the
328 ENTOMOLOGY
known faunae of the earth. Ashmead concurs in the view that the
Hawaiian fauna was originally derived from the Australasian fauna —
the view held by all the specialists who have studied Hawaiian insects.
Geographical Varieties. — Darwin found that wide-ranging species
are as a rule highly variable. The cosmopolitan butterfly Vanessa
cardui presents striking variations in different parts of the earth, largely
on account of climatal differences, as is indicated by the temperature
experiments of several investigators. Standfuss exposed German pupae
of this insect to cold, and obtained thereby a dark variety such as occurs
in Lapland; and by the influence of warmth, obtained a very pale form
such as occurs normally in the tropics only. Our Cyaniris pseudargi-
olus, which ranges from Alaska into Mexico and from the Pacific to the
Atlantic, exhibits many geographical varieties, some of which are
clearly due to temperature, as experiments have shown.
Geographical isolation is often followed by changes in the specific
characters of an organism, as witness the endemic species and varieties
of oceanic islands. Even in the same archipelago, the different islands
may be characterized by different varieties of one and the same species,
or even by different but closely allied species of the same genus. Thus
Darwin and Alexander Agassiz found that in the Galapagos Islands each
island had its own species of Tropidurus (a lizard) and had only one
species, with almost no exceptions. The same phenomenon occurs in
the two Galapagan species of Schistocerca — S. melanocera and 5",
literosa. In melanocera, as Scudder discovered, ''Three or four distinct
types are becoming gradually differentiated on the eight [now ten]
islands from which they are known." Snodgrass, who has made
important additions to Scudder's account, says, in regard to the two
species, "The specimens from the different islands show striking though,
in most cases, slight differences distinguishing the individuals of each
island as a race, from those inhabiting any other island. There are
two exceptions. Abingdon and Bindloe have the same form, and Albe-
marle supports at least two races." Each of these two species presents
no less than five racial types, to which distinctive names have been
applied. Though the relationships and evolution of these races have
been ably discussed by Snodgrass, definite conclusions upon these
subjects are still needed.
Faiinal Realms. — The general distribution of hfe is such that
naturalists divide the earth into several realms, each of which has its
characteristic fauna and flora. As to the precise boundaries of these
faunal realms, zoologists do not all agree, owing chiefly to the fact that
DISTRIBUTION 331
faunfe overlap one another to such an extent as to render their exact
separation more or less arbitrary. Five realms, at least, are generally
recognized: Holarctic, Neotropical, Ethiopian, Oriental and Australian
(Plate III).
The Holarctic realm comprises the whole of Europe, Northern
Africa as far south as the Sahara, Asia down to the Himalayas, and
North America down to Mexico. Though the faunae of all these areas
are fundamentally alike (as Merriam and other authorities maintain),
it is often convenient to divide the Holarctic into two parts: the
Palcearctic, including Europe and most of temperate Asia, being limited
roughly by the Tropic of Cancer; and the Nearctic, occupying almost
the entire continent of North America, including Greenland. The
northern portion of the Holarctic realm forms a circumpolar belt with a
remarkably homogeneous fauna and flora; therefore some authors
distinguish an Arctic realm, limited by the isotherm of 32°, which marks
very closely the tree-limit.
The boreal insects of Eurasia and North America are strikingly
alike. Dr. Hamilton has catalogued almost six hundred species of
beetles as being holarctic in distribution; five hundred of these are com-
mon to Europe, Asia and North America, and the remainder are known
to occur in North America and also in Europe or Asia ; one hundred are
cosmopohtan or sub-cosmopoHtan, to be sure, but fifty of these are
probably holarctic in origin, for example — Dermestes lardarius (larder
beetle) and Tenebrio molitor (meal-worm). Of butterflies, out of some
two hundred and fifty species that are found in the United States east
of the Rocky Mountains, scarcely more than a dozen occur also in the
old world. North of the United States, however, as Scudder finds, no
fewer than thirteen genera are represented in the old world by the same
or by allied species.
The Neotropical realm embraces South America, Central America,
the West Indies and the coasts of Mexico; Mexico being for the most
part a transition tract between the Neotropical and the Nearctic. The
richest butterfly fauna in the world is found in tropical South America.
To this region are restricted, almost without exception, the Euploeinae
and Lemoniinae and over ninety-nine per cent, of the Libytheinae; here
the Heliconiida; and Papilionidse attain their highest development, as
do also the Cerambycidae, or longicorn beetles.
The Ethiopian realm consists of Africa south of the Sahara, Southern
Arabia and Madagascar; though some prefer to regard Madagascar as
a distinct realm, the Lemurian. According to Wallace, the Ethiopian
^3^
ENTOMOLOGY
realm has seventy-five peculiar genera of Carabidae and is marvelously
rich in Cetoniidas and Lycaenidae.
The Oriental realm includes India, Ceylon, Tropical China, and the
Western Malay Islands. In the richness of its insect fauna, this realm
vies with the Neotropical.' Danaidae and Papilionidae are abundant,
while the genus Morpho is represented by some forty species; of Cole-
optera, Buprestidae are important andLucanidae especially so.
The Australian realm embodies Austraha, New Zealand, the Eastern
Malay Islands and Polynesia. Buprestidae are here represented by
forty-seven genera, of which twenty are peculiar; against this showing,
the Oriental has forty-one genera and the Neotropical thirty-nine (Wal-
lace). Strong affinities are said to exist between the Australian and
Neotropical insect faunae.
Life Zones of North America. — Merriam, the chief authority upon
the subject, says: "The continent of North America may be divided.
■^^
tSfS^
v^
^^
\^
/^^
Fig. 299. — Distribution of Erynnis mani-
toba, a butterfly restricted to subarctic and
subalpine regions. — After Scudder.
Fig. 300.— Distribution in the United
States of Eudamus proteus, primarily a trop-
ical butterfly. — After Scudder.
according to the distribution of its animals and plants, into three
primary transcontinental regions — Boreal, Austral and Tropical."
(Plate IV).
The Boreal region covers the northern part of the continent to about
the northern boundary of the United States and continues southward
along the higher portions of the mountain ranges. This region is
divided into three transcontinental zones: (i) the Arctic- Alpine, lying
above the limits of tree growth, in latitude or altitude; (2) the Hudso-
nian, comprising the northern part of the great transcontinental conifer-
ous forest and the upper timbered slopes of the highest mountains of the
United States and Mexico; (3) the Canadian, covering theremainder of
the Boreal region. The butterfly Erynnis manitoha (Fig. 299) is strictly
boreal in distribution.
Plate IV.
DISTRIBUTION 335
The Austral region "covers the whole of the United States and
Mexico, except the Boreal mountains and the Tropical lowlands." It
comprises three transcontinental belts: (i) the Transition zone, in
which the Boreal and the Austral overlap; (2) the Upper Austral; (3)
the Lower Austral. The butterfly Eudamus proteus (Fig. 300) is re-
stricted, generally speaking, to the Tropical region and the warmer and
more humid portions of the Austral.
The Tropical region covers the southern extremity of Florida and
of Lower California, most of Central America and a narrow strip along
the two coasts of Mexico, the western strip extending up into California
and Arizona.
These divisions are based primarily upon the distribution of mam-
mals, birds and plants, and the three primary divisions serve almost
equally well for insects also. In regard to the zones, however, not so
much can be said^ — for insects are to a high degree independent of minor
differences of climate. Many instances of this are given beyond.
The insect fauna of the United States is upon the whole a hetero-
geneous assemblage of species derived from several sources, and the
foreign element of this fauna we shall consider at some length.
Paths of Diffusion in North America. — It may be laid down as a
general rule that every species tends to spread in all directions and does
so spread until its further progress is prevented, in one way or another.
The paths along which a species spreads are determined, then, by the
absence of barriers. The diffusion of insects in our own country has
received much attention from entomologists, especially in the case of
such insects as are important from an economic standpoint. The ac-
cessions to our insect fauna have arrived chiefly from Asia, Central and
South America, and Europe.
Webster, our foremost student of this subject, to whom the author
is indebted for most of his facts, names four paths along which insects
have made their way into the United States: (i) Northwest — Northern
Asia into Alaska and thence south and east; (2) Southwest — Central
America through Mexico ; (3) Southeast— West Indies into Florida ; (4)
Eastern — from Europe, commercially.
Northwest.^ — The northern parts of Europe, Asia and North America
have in common very many identical or closely allied species, whose
distribution is accounted for if, as geologists assure us, Asia and North
America were once connected, at a time when a subtropical climate
prevailed within the Arctic Circle; in fact, the distribution is scarcely
explicable upon any other theory. Curiously enough, the trend of
33(>
ENTOMOLOGY
diffusion seems to have been from Asia into North America and rarely
the reverse, so far as can be inferred.
The lady-beetle, Coccinella quinquenotata, occurring in Siberia and
Alaska, has spread to Hudson Bay, Greenland, Kansas, Utah, CaHfornia
and Mexico; while C. sanguinea, well known in Europe and Asia, ranges
from Alaska to Patagonia ; and Ceratomegilla fuscilahris from Vancouver
and Canada to Chile. About six hundred species of beetles are holarctic
in distribution, as was mentioned. Some of them inhabit different
climatal regions in different parts of their range; thus Lina lapponica in
the Old World "occurs only in the high north and on high mountain
ranges, whereas in North America it extends to the extreme southern
portion of the country," being widely diffused over the lowlands
(Schwarz). Similarly, Silpha lapponica is strictly arctic in Europe, but
is distributed over most of North America ;5i/^/m opaca, on the contrary,
is common all over Europe, but is strictly arctic in North America.
Silpha atrata, common throughout Europe and western Siberia, was
introduced into North America, but failed to estabhsh itself.
Southwest. — Very many species have come to us from Central
America and even from South America. South America appears to be
the home of the genus Halisidota, according to Webster, who has traced
several of our North American species as offshoots of South American
forms. Many of our species may be traced back to Yucatan. H. cinc-
tipes ranges from South America to Texas and Florida; H. tessellaris
has spread northward from Central America and now occurs over the
middle and eastern United States, while a form closely like tessellaris
ranges from Argentina to Costa Rica; H. carycs follows tessellaris, and
appears to have branched in Central America, giving off E. agassizii,
which extends northward into CaHfornia. Similarly in the case of the
Colorado potato beetle {Leptinotarsa decemlineata) and its relatives.
According to Tower, the parent form, L. undecimlineata, seems to have
arisen in the northern part of South America, to have migrated north-
ward and, in the diversified Mexican region, to have spHt into several
racial varieties. The parent form grades into L. multilineata of the
Mexican table lands, which in ttirn, in the northern part of the Mexican
plateau, passes imperceptibly into L. decemlineata, which last species has
spread northward along the eastern slope of the western highlands, west
of the arid region. In the lower part of the Mexican region the parent
form may be traced into L.juncta, which has spread along the low humid
Gulf Coast, up the Mississippi valley to southern Illinois, and along the
Gulf Coast and up the Atlantic coast to Maryland, Delaware and New
DISTRIBUTION 337
Jersey. In general, the mountains of Central America and Mexico and
the plateau of Mexico have been barriers to the northward spread of
many species, which have reached the United States by passing to the
east or to the west of these barriers, in the former case skirting the Gulf
of Mexico and spreading northward along the Mississippi valley or along
the Atlantic coast, in the latter event traveling along the Pacific coast
to California and other Western states. Not a few species, however,
have made their way from the Mexican plateau into New Mexico and
Arizona ; this is true of many Sphingidae. The butterfly A nosia berenice
ranges from South America into New Mexico, Arizona and Colorado;
while many of the Libytheidae have entered Arizona and neighboring
states from Mexico. The chrysomeHd genus Diabrotica is almost ex-
clusively confined to the western hemisphere and its home is clearly in
South America, where no fewer than 367 species are found. About 100
species occur in Venezuela and Colombia, "of which 11 extend into
Guatemala, 8 into Mexico, and i into the United States." We have 18
species of Diabrotica, almost all of which can be traced back to Mexico,
and several of them — as the common D. longicornis — to Central
America. "The common Dynastes tityus occurs from Brazil through
Central America and Mexico, and in the United States from Texas to
Illinois and east to southern New York and New England." Erebus
odora ranges from Ecuador and Brazil to Colorado, Illinois, Ohio, New
England and into Canada, though it is not known to breed in North
America, being in fact a rare visitor in our northern states.
Southeast. — Many South American species have made their way
into southern and western Florida by way of the West Indies, while
some subtropical species have reached Florida probably by following
around the Gulf coast. The semitropical insect fauna of southern and
southwestern Florida, including about 300 specimens of Coleoptera,
according to Schwarz, is entirely of West Indian and Central American
origin, the species having been introduced with their food plants, chiefly
by the Gulf Stream, but also by flight, as in the case of Sphingidae.
Ninety-five species of Hemiptera collected in extreme southern Florida
by Schwarz and studied by Uhler are distinctly Central American and
West Indian in their affinities. Indeed Uhler is inclined to beheve that
the principal portion of the Hemiptera of the United States has been
derived from the region of Central America and Mexico.
Eastern.— On the Atlantic coast are many European species of
insects which have arrived through the agency of man. Most of them
have not as yet passed the Appalachian mountain system, but some
338 ENTOMOLOGY
have worked their way inland. Thus the common cabbage butterfly
{Pieris m/>«), first noticed in Quebec about i860, was found in the north-
ern parts of Maine, New Hampshire and Vermont five or six years later,
was established in those states by 1867, entered New York in 1868 and
then Ohio. Aphodius fossor followed much the same course from New
York into northeastern Ohio, as did also the asparagus beetle {Crioceris
asparagi), the clover leaf weevil {Hyper a punctata), the clover root
borer {Hylastinus obscurus) and other species. In short, as Webster has
pointed out. New York offers a natural gateway through which species
introduced from Europe spread westward, passing either to the north
or to the south of Lake Erie.
Inland Distribution. — Pieris rapce, the spread of which in North
America has been thoroughly traced by Scudder, reached northern New
York in 1868 (as above), but appears to have been independently intro-
duced into New Jersey in 1868, whence it reached eastern New York
again in 1870; it was seen in northeastern Ohio in 1873, Chicago 1875,
Iowa 1878, Minnesota 1880, Colorado 1886, and has extended as far
south as northern Florida, but is apparently unable to make its way
down into the peninsula.
The asparagus beetle, Crioceris asparagi, another native of Europe,
became conspicuous in Long Island in 1856, spread southward to
Virginia and westward to Ohio, where it was taken in 1886; it is fre-
quent now in Illinois and Wisconsin and is known in Colorado and
California. This insect, as Howard observes, flies readily, and may
be introduced commercially in the egg or larval stage on bunches of
asparagus.
The clover leaf weevil, Hypera punctata, common over Europe and
most of Asia, was found in Canada some seventy years ago, has spread
into Mississippi, Texas, Utah and Idaho, and is present on the Pacific
coast also.
The lesser clover leaf weevil, Phytonomus nigrirostris, introduced
from Europe into the United States, has spread steadily westward and
has now reached Illinois, where it has been common since 1919.
Cryptorhynchus lapathi, a beetle destructive to willows and poplars,
and common in Europe, Siberia and Japan, was found in New Jersey in
1882 and in New York in 1896, though known for many years previously
in Massachusetts. It became noticeable in Ohio in 1901, and is steadily
extending its ravages, being known now in Minnesota.
From Colorado the well-known potato beetle {Leptinotarsa decem-
lineata) has worked eastward since 1840, reaching the Atlantic coast,
DISTRIBUTION 339
and has even made its way several times into Great Britain, only to
be stamped out with commendable energy. The box-elder bug {Lep-
tocoris trivittatus) is similarly working eastward, having now reached
Ohio. Formerly the Rocky Mountain locust periodically migrated east-
ward, but always met a check in the moist valley of the Mississippi.
The chinch bug {Blissus leucopterus), the distribution of which has
been traced by Webster, has spread from Central America and Mexico
northward along the Gulf coast into the United States, following three
paths: (i) along the Atlantic coast to Cape Breton; (2) along the
]\Iississippi valley and northward into Manitoba; (3) along the western
coast of Central America and Mexico into Cahfornia and other Western
states. Everywhere this insect has found wild grasses upon which to
feed, but has readily forsaken these for cultivated grasses upon
occasion.
Every year some of the southern butterflies reach the Northern states,
where they die without finding a food plant, or else maintain a precari-
ous existence. Thus Iphiclides ajax occasionally reaches Massachusetts
as a visitor and a visitor only; Lartias philenor, however, finds a limited
amount of food in the cultivated Aristolochia. P. thoas, one of the pests
of the orange tree in the South, is highly prized as a rarity by New Eng-
land collectors and is able to perpetuate itself in the Middle States on the
prickly ash (Xanthoxylum). The strong- winged grasshopper, Schisto-
cerca americand, belonging to a genus the center of whose dispersion is
tropical ; America, ranges freely over the interior of North x\merica,
sometimes in great swarms, and its nymphs are able to survive in
moderate numbers in the southern parts of Illinois, Ohio and other
states of as high latitude, while the adults occasionally reach Ontario,
Canada.
Many species are now so widely distributed that their former paths
of -diffusion can no longer be ascertained. The army worm {Cirphis
unipuncta), feeding on grasses, and occurring all over the United States
south of Lat. 45° 23' N., is found also in Central America, throughout
South America, and in Europe, Africa, Japan, China, India, etc.; in
short, it occurs in all except the coldest parts of the earth, and where it
originated no one knows.
Determination of Centers of Dispersal. — In accounting for the
present distribution of fife, naturalists employ several kinds of evidence.
Adams recognizes ten criteria, aside from palaeontological evidence, for
determining centers of dispersal:
I. Location of greatest dififerentiation of a type.
340 ENTOMOLOGY
2. Location of dominance or great abundance of individuals.
3. Location of synthetic or closely related forms (Allen).
4. Location of maximum size of individuals (Ridgway-AUen) .
5. Location of greatest productiveness and its relative stability,
in crops (Hyde).
6. Continuity and convergence of lines of dispersal.
7. Location of least dependence upon a restricted habitat.
8. Continuity and directness of individual variations or modifica-
tions radiating from the center of origin along the highways of dispersal.
9. Direction indicated by biogeographical affinities.
10. Direction indicated by the annual migration routes, in birds
(Palmen).
2. Geological
Means of Fossilization. — Abundant as insects are at present, they
are comparatively rare as fossils, the fossil species forming but one per
cent, of the total number of described species of insects. The absence
of insect remains in sedimentary rocks of marine origin is explained by
the fact that almost no insects inhabit salt water; and terrestrial forms
in general are ill-adapted for fossihzation. The hosts of insects that die
each year leave remarkably few traces in the soil, owing perhaps, in
great measure, to the dissolution of chitin in the presence of moisture.
Most of the fossil insects that are known have been found in vege-
table accumulations such as coal, peat and lignite, or else in ancient
fresh-water basins, where the insects were probably drowned and
rapidly imbedded. At present, enormous numbers of insects are
sometimes cast upon the shores of our great lakes — a phenomenon which
helps to explain the profusion of fossil forms in some of the ancient
lake basins.
Insects in rich variety have been preserved in amber, the fossilized
resin of coniferous trees. This substance, as it exuded, must have en-
tangled and enveloped insect visitors just as it does at present. Many
of these amber insects are exquisitely preserved, as if sealed in glass.
Copal, a transparent, amber-like resin from various tropical trees, par-
ticularly Leguminosae, has also yielded many interesting insects.
Ill-adapted as insects are by organization and habit for the com-
moner methods of fossilization, the number of fossil species already
described is no fewer than three thousand.
Localities for Fossil Insects.^ — The Devonian of New Brunswick
has furnished a few forms, found near St. John, in a small ledge that
DISTRIBUTION 34I
outcrops between tide-marks; these forms, though few, are of extraor-
dinary interest, as will be seen.
For Carboniferous species, Commentry in France is a noted locality,
through the admirable researches of Brongniart, who described from
there 97 species of 48 genera, representing 12 families or higher groups,
10 of which are regarded as extinct; without including many hundred
specimens of cockroaches which he found but did not study. In this
country many species have been found in the coal fields of Illinois,
Nova Scotia, Rhode Island, Pennsylvania and Ohio.
Many fine fossils of the Jurassic period have been found in the litho-
graphic limestones of Bavaria; 143 species from the Lias — four fifths of
them beetles — were studied by Heer.
The Tertiary period has furnished the majority of fossil specimens.
To the Oligocene belong the amber insects, of which 900 species are
known from Baltic amber alone, and to the same epoch are ascribed the
deposits of Florissant and White River in Colorado and of Green River,
Wyoming. These localities — the richest in the world — have been made
famous by the monumental works of Scudder. At Florissant there is an
extinct lake, in the bed of which, entombed in shales derived from vol-
canic sand and ash, the remains of insects are found in astonishing pro-
fusion. For Miocene forms, of which 1,550 European species are
known, the QEningen beds of Bavaria are celebrated as having furnished
844 species, described by the illustrious Heer.
Pleistocene species are supplied by the peats of France and Europe,
the lignites of Bavaria, and the interglacial clays of Switzerland and
Ontario, Canada.
Silurian and Devonian. — The oldest fossil insect known consists of
a single hemipterous wing, Protocimex, from
the Lower Silurian of Sweden. Next in age
comes a wing, PalaoUaUina (Fig. 301), of
doubtful position,^ from the Middle Silurian
of France. Following these are six specimens fig. 301.— Paiaobiattina
of as many remarkable species from the Devon- gfotS'iAR?^'^^ size.-After
ian shales of New Brunswick. The specimens,
to be sure, are nothing but broken wings, yet these few fragments,
interpreted by Dr. Scudder, are rich in meaning. All are neuropteroid,
but they cannot be classified satisfactorily with recent forms on account
of being highly synthetic in structure. Thus Platephemera antiqua (Fig.
* There is some evidence, it should be said, that this species is not an insect. Handlirsch
denies also that Protocimex is an insect.
342
ENTOMOLOGY
302), though essentially a May fly of gigantic proportions (spreading
probably 135 mm.), has an odonate type of reticulation; while Xenoneura
(Fig. 303) combines characters which are now distributed among Ephe-
meridas, Sialidas, Rhaphidiidae, Coniopterygidas, and other families,
besides being in many respects unique. These Devonian forms attained
huge dimensions as compared with their recent representatives; Gere-
phemera, for example, had an estimated expanse of 175 millimeters.
Fig. 302. — Platephemera antiqua, natural size. — After Scudder.
Fig. 303. — Xenoneura antiquorum, five times natural size. — After Scudder.
Carboniferous. — The Carboniferous age, with its luxuriant vegeta-
tion, is marked by the appearance of insects in great number and variety,
still restricted, however, to the more generaHzed orders. The domi-
nance of cockroaches in the Carboniferous is especially noteworthy, no
fewer than 200 Palaeozoic species being known from Europe and North
America. These ancient roaches (Fig. 304) differed from their modern
descendants in the similarity of the two pairs of wings, which were alike
in form, size, transparency and general neuration, with six principal
nervures in each wing; while in recent cockroaches the front wings have
become tegmina, with certain of the veins always blended together,
though the hind wings have retained their primitive characteristics with
a few modifications, such as the expansion of the anal area. Carboni-
ferous cockroaches furthermore exhibit ovipositors, straight, slender,
and half as long again as the abdomen — organs which do not exist in
recent species.
DISTRffiUTION
343
Lithomantis (Fig. 305), a remarkable form from Scotland, possessed
in addition to its four large neuropteroid wings, a pair of prothoracic
Fig. 304. — Eloblatlina ma- Fig. 305. — Lithomantis carbonarius, showing protho-
zona, a Carboniferous cock- racic appendages. Two thirds natural size. — After WooD-
roach from Illinois. Twice ward.
natural size. — After Scudder
in Miall and Denny.
Fig. 306. — Stenodictya lobata, showing wing-like appendages of prothorax and abdomen.
Natural size. — After Handlirsch.
wing-like appendages which, provided they may be regarded as homolo-
gous with wings, represent a third pair, either atrophied or undeveloped
344 ENTOMOLOGY
— a condition which is never found today, unless the patagia of Lepidop-
tera represent wings, which is unhkely.
Stenodidya lohata (Fig. 306) described by Brongniart from the
Upper Carboniferous of Commentry, France, also bears prothoracic
"wings" and, in addition, eight pairs of abdominal wing-like or gill-like
appendages. No fewer than five families of Palaeozoic insects are
represented by specimens having prothoracic wings.
From the rich deposits of Commentry, Brongniart has described
several forms of striking interest. Dictyoneura is a Carboniferous genus
Fig. 307. — Eugereon bockingi. Three quarters natural size. — After Dohrn.
with neuropteroid wings and an orthopteroid body, having, in common
with several contemporary genera, strong isopteran affinities. Coryda-
loides scudderi, a phasmid, has an alar expanse of twenty-eight inches.
The Carboniferous prototypes of our Odonata were gigantic beside their
modern descendants, one of them {Meganeura) having a spread of more
than two feet; they were more generalized in structure than recent
Odonata, presenting a much simpler type of neuration and less differen-
tiation of the segments of the thorax. The Carboniferous precursors of
our May flies attained a high development in number and variety; in
fact, the Ephemeridae, like the Blattidae, achieved their maximum
development ages ago, when they attained an importance strongly con-
trasting with their present meager representation.
The Permian has supplied a remarkable genus Eugereon (Fig. 307)
DISTRIBUTION 345
with hemipterous mouth parts associated with filiform antennaj and
orthopteroid wings. The earliest unquestionable traces of insects with
an indirect metamorphosis are found in the Permian of Bohemia, in
the shape of caddis-worm cases.
Triassic. — Triassic cockroaches present interesting stages in the
evolution of their family. Through these Mesozoic species the con-
tinuity between Palaeozoic and recent cockroaches is clearly established
— which can be said of no other insects; and in fact of no other animals,
the only comparable cases being those of the horse and the moUuscan
genus Planorhis. In the Triassic period occur the first fossils that can be
referred indisputably to Coleoptera and Hymenoptera, the latter order
being represented first, as it happens, by some of its most specialized
members, namely ants.
Jurassic. — At length, in the Jurassic, all the large orders except Lep-
idoptera occur; Diptera appear for the first time, and Odonata are rep-
resented by many well-preserved specimens, while the Liassic
Coleoptera studied by Heer number over one hundred species. The
Cretaceous has yielded but few insects, as might be expected.
Tertiary. — In the rich Tertiary deposits all orders of insects occur.
Baltic amber has yielded Collembola, some remarkable Psocidae, many
Diptera, and ants in abundance. Of 844 species taken from the noted
Miocene beds of OEningen, nearly one half were Coleoptera, followed by
neuropteroid forms (seventeen per cent.) and Hymenoptera (fourteen
per cent.) ; ants were twice as numerous in species as they are at present .
in Europe. Almost half the known species of fossil insects have been
described from the Miocene of Europe. To the Miocene belongs -the
indusial limestone of Auvergne, France, where extensive beds — in some
places two or three meters deep — consist for the most part of the cal-
cified larval cases of caddis flies.
At Florissant, as contrasted with Q^ningenby Scudder, Hymenoptera
constitute 4.0 per cent, of the specimens, owing chiefly to the predomi-
nance of ants; Diptera follow with 30 per cent, and then Coleoptera with
13 per cent. Modern famihes are represented in great profusion. The
material from Florissant and neighboring locahties includes a Lepisma,
fifteen species of Psocidae, more than thirty species of Aphididae, and
more than one hundred species of Elateridae, while the Rhynchophora
number 193 species as against 150 species from the Tertiary of Europe.
Tipulidae are abundant and exquisitely preserved, while Bibionidae, as
compared with their present numbers, are surprisingly common. Nu-
merous masses of eggs occur, undoubtedly sialid and closely like those of
346 ENTOMOLOGY
Corydalis. Sialid characters, indeed, appear in the oldest fossils known,
and are strongly manifest throughout the fossil series, though among
recent insects Sialidae occupy only a subordinate place. Strange to say,
few aquatic insects have been found in this ancient lake basin.
Fossil butterflies are among the greatest rarities, only seventeen
being known; yet Florissant has
contributed eight of these, a few of
which are marvelously well pre-
served (Fig. 308), as appears from
Scudder's figures. Two of the
Florissant specimens belong to
Libytheinae, a group now scantily
represented, though widely distri-
buted over the earth. The group
is structurally an archaic one, and
Fig. 308. — Prodryas persephone, a fossil its recent members (forming only
butterfly from Colorado. Natural size. — •1.1 1 i.i r .-i •, m i
After ScuDDER. One eight-hundredth of the described
species of butterflies) are doubtless
relicts.
Taken as a whole, the insect facies of Tertiary times was apparently
much the same as at present. The Florissant fauna and flora indicate,
however, a former climate in Colorado as warm as the present climate
of Georgia.
Quaternary. — The interglacial clays of Toronto, Ontario, have yielded
fragments of the skeletons of beetles to the extent of several hundred
specimens, about one third of which (chiefly elytra) were sufficiently
complete or characteristic to be identified by Dr. Scudder, who found in
all 76 species of beetles, representing 8 families, chiefly Carabidae and
Staphylinidae. All these interglacial beetles are referable to recent
genera, but none of them to recent species, though the differences
between the interglacial species and their recent alHes are very slight.
As a whole, these species "indicate a climate closely resembling that of
Ontario to-day, or perhaps a sHghtly colder one One cannot
fail, also, to notice that a large number of the allies of the interglacial
forms are recorded from the Pacific coast." (Scudder.) The writer,
who has studied these specimens, has been impressed most by their
Hkeness to modern species. It is indeed remarkable that so little
specific differentiation has occurred in these beetles since the inter-
glacial epoch — certainly ten thousand and possibly two to three hundred
thousand years ago.
DISTRIBUTION 347
General Conclusions. — Unfortunately, the earliest fossils with
which we are acquainted shed much less light upon the subject of insect
phylogeny than one might expect. The few Devonian forms, though
synthetic indeed as compared with their modern allies, are at the same
time highly organized, or far from primitive, and their ancestors have
been obliterated.
The general plan of wing structure, as Scudder finds, has remained
unaltered from the earliest times, though the Devonian specimens
exhibit many peculiarities of venation, in which respect some of them are
more specialized than their nearest living allies, while none of them
have much special relation to Carboniferous forms.
Carboniferous insects are more nearly related to recent forms than are
the Devonian species, but present a number of significant generalized
features. Generally speaking, the thoracic segments were similar and
unconsolidated, and the two pairs of diaphanous wings were alike in
every respect — in groups that have since developed tegmina and dis-
similar thoracic segments. The Carboniferous precursors of our cock-
roaches, phasmids and May flies have been mentioned. Palasozoic
insects were grouped by Scudder into a single order, Palaeodictyoptera, on
account of their synthetic organization, though other authors have tried
to distribute them among the modern orders. This disagreement will
continue until, with increasing knowledge, our classification becomes
less arbitrary and more natural.
Mesozoic insects are interesting chiefly as evolutionary links,
notably so in the case of cockroaches — the only insects whose ancestry
is continuously traceable. In this era the large families became differen-
tiated out.
Most of the Tertiary species are referable to recent genera, peculiar
famihes being highly exceptional, while all the Quaternary species
belong to recent genera.
Hemiptera appear in the Silurian; Neuroptera (in the old sense) in
the Devonian; Thysanura and Orthoptera, Carboniferous; Coleoptera
and Hymenoptera, Triassic; Diptera, Jurassic; and Lepidoptera not
until the Tertiary.
Since Scudder's day, considerable additions to the knowledge of our
fossfl insects have been made by Professor T. D. A. Cockerell and
by Professor H. F. Wickham.
A comprehensive and richly illustrated account of fossil insects is
given by Handlirsch in his great work. Die fossilen Insekten.
CHAPTER XIII
INSECT ECOLOGY
Ecology is the physiology of organisms in relation to environment.
It is the physiology of entire organisms rather than of organs. It deals
with, the reactions of organisms to the conditions of their existence,
including the modification of these reactions in relation to changes of
environment.
Though its subject matter is primarily animals and plants, ecology
is based upon all the sciences, and cannot be pursued most precisely
without the aid of some mathematics.
Insect life in its omnipresence and diversity affords countless illus-
trations of ecological principles, under which innumerable isolated
observations fall into organization.
The qualitative study of the subject is simply a matter of accurate
and thorough observation and correct inference, with the aid of the
simplest kind of experimentation. Even in quantitative investigation,
the ecological principles may be brought out with the use of such
inexpensive means as thermometers, ice-boxes, weather maps, etc.
For the most refined work, however, elaborate appliances for controlling
ecological factors are often necessary.
It should be remembered that the study of insects alone gives only
a partial understanding of ecology, with an imperfect perspective of
the subject.
The ecology of individuals is known as Autecology; that of com-
munities, as Synecology.
I. Conditions of Terrestrial Existence
I. Soil
The edaphic conditions of existence (those relating to the soil) are
the same for animals and plants, but are utiHzed in different ways by
these organisms. Plants can utilize inorganic constituents of the soil
as food, but animals can not. All the food of animals, with such
exceptions as water and salt, is derived in the last analysis from plants.
Structure. — The retention of water by the soil depends largely upon
the size of the soil particles; soil of small particles holding more water
348
INSECT FXOLOGY 349
than one of large particles. Water evaporates more rapidly from
coarse soils than from fine ones, but in loose soils the more rapid evapora-
tion from the surface forms an aerated "mulch" which retards further
evaporation. The different capacities of different soils for absorbing
or retaining moisture affects insects indirectly by its effects on vegetation,
or may affect them directly. The compactness of loose soils varies with
the amount of water present, which is of importance to burrowing insects.
A good example of this is seen in the sandy beach of a lake, when the
sand wet by waves becomes firm; the water evaporates rapidly, however,
until the sand is dry again, in proportion to its nearness to the surface.
In such sand, with frequent alternations from wet to dry, insects do not
live; though some forms, as tiger beetles and beetles of the genus
Bembidion, burrow in the sand a little farther back from the shore,
where the fluctuations in the water content are not so great.
In a loose soil white grubs or wireworms go easily and rapidly from
one plant to another. Tiger beetles and ants need soil of a consistence
which will maintain the burrows after they are made. Caterpillars,
grubs, etc., about to pupate, can not burrow in soil that is too hard, and
frequently avoid also soil that is too loose. The bollworm if unable to
dig into hard baked soil will enter cracks in the soil. Some grasshoppers,
on the other hand, prefer hard-packed soil in which to lay their eggs.
In making their pupal cells in the ground, larvae press the surrounding
soil into a compact wall, often adding a cementing fluid which is fre-
quently waterproof. The bollworm, or corn ear worm, lines its burrow
with silk.
A soil of loose texture faciHtates the emergence of adult insects.
If the soil is too hard they may not be able to emerge until it has been
softened by rain. Plowing and roUing the soil of a stubble field in
summer is known to prevent the exit of Hessian flies.
The depth to which insects burrow in the ground depends upon the
physical nature of the soil, and temperature and moisture as well.
Chemical Conditions. — In addition to oxygen, carbon dioxide
and nitrogen, the soil contains other gases and various chemical com-
pounds, some of which are essential to plant life and therefore indirectly
to the welfare of animals. The character of the vegetation as determined
by the acidity or alkalinity of the soil affects the character of the insect
fauna. The acid water of bogs is directly unfavorable to insect life,
but is favorable to the growth of peculiar plants which are selected as
food by certain insects. In New Jersey, Mr. H. Bird, by acidulating
soil with an artificial bog water made with the extract of hemlock used
350 ENTOMOLOGY
for tanning leather, succeeded in growing the pitcher plant, Sarracenia
purpurea, and in raising thereon a species of rare moth, Papaipema
appassionata, known for thirty years only by a unique type in the
British Museum.
Plants of alkaline desert soils have their characteristic insect fauna.
Air.- — The oxygen content of subterranean air is important directly
for respiration; indirectly for its effects on vegetation. Aeration of the
soil is essential to subterranean life. In too compact a soil insects
suffer from lack of oxygen and excess of carbon dioxide, and may
experience also the effects of excessive evaporation and mechanical
difficulties in burrowing.
Water. — For their welfare, soil insects must have neither too much
nor too httle water. They may be drowned by gravitational water,
which acts also by fiUing the air spaces around soil particles. Sub-
mersion was used effectively in France against the destructive Phyl-
loxera of the grape. Capillary water is, on the contrary, favorable to
the insect life until it evaporates to excess. As with terrestrial insects,
the vital effects of water and temperature are produced through
evaporation, in relation to which soil forms exhibit various adaptations.
As the soil dries, ants dig deeper. The depth of pupal chambers,
their compact waterproofed walls, and the air space around the pupa,
and the closing of the entrance to the burrow, all tend to protect the
pupa from undue loss of bodily moisture.
With the tiger beetles, the amount of moisture determines whether
eggs are to be laid, and their number if laid; eggs being absent in dry
soil (Shelford).
Temperature.— There are great differences in the temperatures of
different soils, from dry sands to moist shaded humus. Temperature
and moisture determine largely the character of the flora and of the
accompanying fauna. The greater the depth of soil the lower the tem-
perature as a rule. Ants and other insects will dig deeper to avoid heat
as well as dryness. Ants often find suitable conditions of temperature
and moisture under stones or logs.
In the case of insects that are said to be killed by heat, the mortality
is due primarily to evaporation and secondarily to the coagulation of the
protoplasm; perhaps also to ultra-violet rays.
Physiographic Conditions. — As environmental factors there must
be considered also the nature of the surface of the soil as regards exposure
or cover, the slope of the soil, and the altitude at which it is found.
All these things affect the fauna. Angle of slope has an effect in
INSECT ECOLOGY 35 I
determining the presence or absence of oviposition burrows of tiger
beetles, and the presence, absence, or number of eggs laid (Shelf ord).
Nutriment. — The food of soil insects may be roots or stems of
plants, dead animal or vegetable matter, other insects or other animals.
Some insects are parasitic on burrowing mammals. Many ants derive
part of their nourishment from the root-sucking aphids or coccids
which they attend. Ants and termites sustain diverse relations as
regards food with various other insects and other arthropods that live
in their nests. Some species that burrow near the surface, as tiger
beetles and ant-lions, capture their prey from the surface of the ground.
Soil that contains no organic matter, as pure quartz sand, is food
for no insect. Some larvae, as white grubs and wireworms, that subsist
primarily on roots of plants, can if necessary thrive for many months on
a diet of soil alone, but only because of the organic matter that it
contains.
Interactions. — The subject of interactions in the soil environment
can only be touched upon here. The character of the soil itself is
changed by the plants and animals that inhabit it. Thus burrowing
animals, as worms, crawfishes, insects, moles, mice, many larger
mammals, etc., alter the distribution and the physical and chemical
composition of the soil. Bacteria and fungi play important parts.
The soil is not fully effective in protecting its insect inhabitants from
predaceous and parasitic enemies among other insects, and soil insects
are themselves food for many birds, mammals, and other of the larger
animals.
2. Atmosphere
The most conspicuous effect of hght is its directive effect on locomo-
tion. This phenomenon is discussed in another chapter (p. 306),
where it is shown that insects react either positively or negatively to
light, are often attuned to definite ranges of light intensity, and react
differently to hght of different wave lengths. The results of photo-
tropism are often incidentally adaptive. As examples, the positive
reaction may take insects to their food, cause the nuptial flight of ants
or termites, or the swarming of bees; while the negative response may
lead insects into places of concealment, pupation, or hibernation.
Structures and functions are correlated with the presence or the absence
of light; for example, those of the eyes. Insects that Kve in darkness,
as boring species, subterranean forms, and cave insects, exhibit special
352 ENTOMOLOGY
modifications in relation to the absence of light that are mentioned in
other parts of this book.
Growth.- — In nature the effects of light on growth are bound up
with those of temperature. The temperature of the air varies with
light {insolation, or exposure to the sun's rays) . Cloudy summer days
are cooler than sunny days. Cloudy winter days are warmer. (Shel-
ford.) Light affects the rate of growth, or more precisely, some wave
lengths are more effective than others. Beclard reared larvae of the
flesh-fly, Musca carnivora, from the eggs, under glass bells of different
colors. The largest larvae were found under violet or blue; the smallest
under green; the colors producing their effects in the following order:
violet, blue, red, yellow, white, green. Under violet the larvas were
three-quarters greater than under green. Green rays retarded growth,
as did also white light. (C. B. Davenport.)
Activity. — Sunshine, aside from temperatures, unless they are
extreme, has a stimulating effect on reproduction and other activities
in flies (Bishopp, Dove, Parman) ; and this is true probably for most
diurnal insects. On cloudy days the boll weevil and most other
insects as well are less active than on clear days, without regard to
temperature.
Exposure to hot sunshine kills pupae of the bollworm, plum curculio
and other forms. This result is due primarily to heat with evaporation,
but possibly the ultra-violet rays also exert some influence.
Sleep.- — Whatever the temperature may be, insects go to sleep when
■ night falls, and do so during the daytime if clouds diminish the sunlight
beyond a certain point which varies for different species. If it becomes
very cloudy, the mourning-cloak, Vanessa antiopa, seeks some crevice
and goes to sleep, but is quickly aroused, however, by returning sun-
shine. The sleep of insects doubtless has the same physiological
results as that of other animals.
"A few species seem to choose protectively colored situations, and
others select sites which are in various ways protective. Some which
are solitary by day are gregarious at night, and some insects sleep with
all the regularity of a theoretical modern infant, while others of a more
unsystematic life snatch a wink when they can. " (P. Rau and N. Rau.)
Temperature
Temperature Limits. — It goes without saying that the life-processes
and the activities of every animal or plant are confined within a certain
range of temperature, outside of which the organism cannot exist.
INSECT ECOLOGY 353
This range is different for different species, for the same species in differ-
ent seasons or places, and is different even for different individuals of
the same species under apparently equal conditions, and for different
stages in the growth or development of the same individual. The
temperature-range is affected by food, moisture, evaporation, and
several other factors.
Growth and development proceed most rapidly in a certain optimum
range of temperature, within which there is, at least theoretically, an
optimum degree of temperature. At and above a certain degree of
high temperature heat-rigor sets in, and may or may not be fatal to an
organism, according to the duration of the exposure to the temperature.
This maximimi temperature has as its upper limit the uUramaximum,
at which the organism dies at once, probably because of the coagulation
of proteids in the protoplasm. At a certain degree of low temperature,
cold-rigor takes place; the point at which it occurs being near the freez-
ing point, on account of the fluid content of protoplasm. Below this
minimum is an ultraminimum temperature, at which the organism dies.
The following examples of temperature-limits are from Davenport's
Experimental Morphology.
Insect Maximum Ultramaximum
Springtail, Podiira similata 27° C. 36.0° C,
Mosquito, Culex pipiens 40° C.
Larva of fly, Musca vomitoria , 42 . 5° C.
Pupa of fly, Musca vomitoria 43 . 7° C.
Silkworm, Bombyx mori 42 . 5° C.
Back-swimmer, Notoneda 45 . 0° C.
It should be noted that the Podura (near Achorutes) has a thin
integument, and can not live in a dry atmosphere. The pupa of the
fly is protected somewhat by its puparium, and the back-swimmer by
a fairly thick integument.
Insect Ultraminimum
Honey bee, Apis mellifera — i . 5° C.
House fly, Musca domestica — 5 . 0° C.
Larva of cockchafer, Melolontha — 15 .0° C.
Adult cockchafer, Melolontha — 18 . 0° C.
Davenport notes that the large size and thick covering of the beetle,
Melolontha prevent the rapid loss of heat.
Activity in Relation to Temperature. — The range of activity of the
adult cotton boll weevil lies between 56° F. and 95° F. From 95° to
122° is the range of aestivation, within which the beetles are inactive.
From 122° to 140° (soil temperature) is an upper range of fatal tem-
23
354 ENTOMOLOGY
peratures, in which the weevil dies in 15 minutes to i second, according
to the temperature, 140° being the maximum fatal temperature.
In the descending scale of temperature, there is a range between 56°
to 24° within which the beetles hibernate. Below 24° is the lower range
of fatal temperatures, with 7° as the minimum fatal temperature. As
the hmits of these ranges vary with moisture and other factors, these
ranges, as given by Hunter and Pierce (191 2) are necessarily approxima-
tions; but they serve to illustrate the fact that such ranges exist, and
are accurate for the particular conditions under which they were made.
It may be mentioned that Hunter and Pierce found that the winter
cold is, on the average, almost twice as effective as summer heat in
kilhng the beetle; which has several times been greatly reduced in
numbers by early freezes in the South.
High temperatures are more favorable to the activities of insects
than to those of human beings. The temperature range of activity
varies with different species.
The effect of temperature upon the locomotor activity of the boll
weevil was tested by Dr. A. W. Morrill, who found that as the tem-
perature was gradually raised the activity of the weevils increased up
to 105° F. At 95° the beetles were very active; at 86° they began to
lose their activity; and at 37° all movement ceased. Out of doors,
weevil activity began and ceased at about 75°; feeding continuing at
lower temperatures than oviposition.
The number of daily feeding punctures of the weevil was found to be
greatest at about 80° F., as was also the number of eggs laid. (Hunter
and Hinds.)
The curve representing the average number of eggs deposited daily
by the alfalfa weevil, Phytonomus posticus, follows the curve of the mean
daily temperature in all its major fluctuations, the highest record
(twenty-six eggs) occurring on the day (May 18) with the highest mean
temperature (72° F.) of any day previous to June 6. (T. H. Parks.)
By stimulating the activities of insects, high temperatures diminish
the longevity. Thus a worker honey bee that hibernates may live for
six or seven months, but an active worker in summer lives only five or
six weeks.
Other things being equal, the longevity of insects in general is
lengthened by a decrease in temperature and shortened by an increase
(when these temperatures are between about 42° and 72° F.) ; the differ-
ence in longevity of a species at different temperatures corresponding
roughly to the difference in temperature. (J. P. Baumberger.)
INSECT ECOLOGY
355
Development in General.^The effects of temperature on the
development of insects are known in a qualitative way, and considerable
progress has been made in the quantitative study of the subject. At
a certain degree of low temperature during development an insect
becomes physiologically inactive, or dormant, without being killed,
and may resume activity when the temperature rises. This point
is termed the threshold of development {critical point, developmental
zero). Temperatures above this point that are conducive to develop-
ment are termed effective temperatures, and in ascertaining the number
of temperature units requisite to development, all temperatures below
the threshold of development are disregarded. The effects of high
temperatures in accelerating development, and of low temperatures in
retarding development, are known to all who have raised butterflies
or moths from pupae.
The theory used to be that the entire development of an insect,
from the time the egg is laid until the adult emerges, requires a fixed
number of effective degrees of temperature; the same being true also
for any stage of the insect, as egg, larva or pupa; that the entire develop-
ment, or any phase of the development, will not be completed until a
definite number of temperature units have been experienced, whether
the time required be long or short. The number expressing the total
temperature, or temperature constant, is obtained by multiplying the
mean daily temperature by the number of days required for the develop-
ment. Needless to say, the effects of temperature are obscured by
those of humidity, light, and several other influences in nature, and
become evident only under the exact conditions of experimentation.
For the development of the boll weevil, Hunter and Hinds (1905)
give the following summary:
Average
Average 1
Total
1 Total
period
effective
effective
Stage
observations
for stage,
temperature,
temperature,
Days
°F.
°F.
Egg 616
4.0
34-0
136.0
Larva 313
9.8
32.2
315-6
Pupa 530
S-S
33-2
182.6
Total development, sum of stages i , 459
193
32.9
634.2
Observations on entire period of
development 887
19.6
32.2
632.0
temperati
356 ENTOMOLOGY
Exact experimental studies of the effects of temperature, moisture,
and other conditions have undoubtedly an important economic bearing.
For example: it was found, from experiments made by Professor. T. J.
Headlee in Manhattan, Kansas, that the cycle of the codUng moth
required an average of 39 days with an average of 1,006 degrees of
effective temperature (temperatures above the threshold of develop-
ment, given at that time as about 50° F.). With as exact a knowledge
of the other factors, particularly moisture, one ought to be able, with
the aid of weather reports, to foretell when a given brood of the cod-
ling moth will appear; which would evidently be of advantage to
fruit-growers.
The subject is, however, not so simple as it was thought to be.
Sanderson (1908, 1910), who has given a useful discussion of this sub-
ject, showed "that upon purely theoretical grounds there could be
no uniform accumulation of temperature or 'thermal constant' for the
various stages of insect growth, but that the relation of temperature to
growth phenomena was probably different for each species and might
be expressed by a curve, the abscissas of which represent degrees of
temperature and the ordinates represent the time factor. The impor-
tance of considering the so-called law of the velocity of chemical reaction
as influenced by temperature was pointed out and it was shown that the
velocity of reaction varies at different temperatures. It was shown
that both the so-called thermal constant and coefficient of velocity
increase as the temperature is lowered from the optimum of the species,
and that the curve for each species and phase of growth or activity of
that species must be plotted before the influence of temperature can be
exactly stated." Sanderson defined the " thermal constant" for insects
as "that accumulation of mean daily temperature above the 'critical
point' of the species, which will cause it to emerge from hibernation or
to transform from any given stage." (i)There is no uniform minimum
above which the temperature may be accumulated as effective, but this
varies with each species and phase of growth; (2) there is no "thermal
constant" as far as a mere accumulation of temperatures is concerned;
and (3) the velocity of reaction varies according to the range of tem-
peratures (Sanderson) . To illustrate the first of these three statements,
Sanderson cites the green-bug, Toxoptera graminum, which, as Hunter
and Glenn showed, begins to develop at 1.65° C, while its parasite,
Lysiphlebus tritici, shows no activity below about 4° or 5° C. For the
bollworm the point of cold rigor is about 10° C. In regard to the second
statement, Sanderson adds: "It is evident that any accumulation of
INSECT ECOLOGY 357
temperature to secure a thermal or physiological constant cannot be
based on a mere addition where variable temperatures are involved, for
it is evident that every degree has a different value in relation to the
time factor. Thus as the mean temperature rises with the advance of
the season both the time for the pupal stage and the total accumulated
temperature for the pupal stage of the codhng moth decrease with the
advancing season. Though a fairly constant 'total effective tem-
perature' for any given phase of an insect's hfe or activity may be
secured for the summer months when there is a fairly constant mean
temperature, such an accumulation will have no meaning in regard
to the same phenomena in spring and fall when the temperatures are
more variable. If we wish to be exact, we must secure the temperature
curve for the species, based on the observation of a considerable num-
ber of individuals kept at different constant temperatures, or possibly
better at temperatures having a diurnal variation with constant maxi-
mum and minimum, and with fairly constant moisture conditions."
Krogh on Temperature-velocity.— The results obtained by Krogh,
which differ in some respects from those of other investigators, are
regarded as highly important. He finds that the temperature-velocity
curve expressing the rate at which segmentation takes place in frog's
eggs is, between 7° and 20.7°, a straight line. "An increase in tem-
perature between these limits produces a proportional increase in the
velocity with which the processes in the egg leading up to segmentation
take place. Below 7° the curve deviates from the straight line and the
reaction takes place more rapidly than one would expect from the
results obtained at higher temperatures. At the lowest temperature,
where the development certainly is no longer normal the curve turns
downward once more."
"The relation between the temperatures and the velocity of embry-
onic development is algebraic over a range of temperatures which
corresponds approximately to that at which normal development can
take place, and the curve representing the relation is consequently a
straight Hne." The velocity of embryonic development is a linear
function of the temperature.
In regard to the relation between temperature and the later stages of
development of the frog, Krogh says: "Between the temperatures 12°
and 25° the increment in velocity of the embryonic development of the
frog is therefore proportional to the temperature increment, but below
12° the development is more rapid than one would expect from the
formula."
358 ENTOMOLOGY
Concerning the time of incubation of the eggs of a water beetle,
Acilius sulcatus, Krogh found that "when the reciprocal values of the
hatching times at the three temperatures are plotted against the tem-
peratures, they are found to lie in a straight line." (See also Krogh's
results on Pupal Development, p. 359.)
From all that has been said, then, it appears that there is a threshold
of development, which varies for different species and under different
conditions of existence, and that there is such a thing as an accumulation
of effective temperatures, or thermal constant. This constant is lim-
ited, however, to a certain range of temperature, below which growth or
development is faster than the constant requires, and above which it is
slower. This fact has an economic consequence; for basing predictions
upon the thermal constant alone, the spring brood of the codHng moth
or other insect would appear earlier than would be expected, and the
autumn brood later.
Reproduction. — Among plant lice parthenogenesis (reproduction
without fertilization) is apparently continuous and uninterrupted under
favorable environmental conditions; amphigony (reproduction by fertili-
zation) occurring only under the influence of low temperatures and,
as certain authors claim, inadequate food supply. Aphids in tropical
and other warm climates appear to have the tendency to reproduce
exclusively by parthenogenesis. The same condition apparently obtains
among greenhouse aphids in temperate climates. Aphids in colder
climates undergo heterogony (reproduction both by parthenogenesis
and amphigony) as an adaptation to adverse environmental conditions.
In certain species, the appearance of the amphigonous generation seems
to be a rhythmic process, which continues to occur at definite cyclical
intervals for some time after the influence of low temperature has been
eliminated. (L. B. Uichanco.)
Incubation. — The length of the egg period varies greatly according
to surrounding conditions, chiefly those of temperature. First brood
eggs of the codHng moth in Michigan hatched at outdoor temperatures
in 4 to 10 days, average 8 days, at an average mean temperature of
about 67.6° F.; eggs not hatching readily, however, during extremely
dry weather. (A. G. Hammar.)
In regard to the eggs of this species, C. B. Simpson says: " (i) Under
a low temperature the length of the egg stage is longer than at high
temperatures. (2) Under normal field conditions a small difference
in temperature causes but Httle change in the length of the stage. (3)
INSECT ECOLOGY 359
The eggs are not in the same stage of maturity at the time of oviposition,
as at 24° F. we have from 9 to i8 days as the length of the stage."
As regards the threshold of development, Sanderson found that eggs
of the meal worm, Tenehrio molitor> failed to hatch at 9° or 10° C. but
hatched at 12° C.
The time from the deposition of the eggs to hatching of the chinch
bug' is variable, being longer if temperature is low, or shorter if high.
Thus first brood eggs (June) with an average mean temperature of 73° F.
hatch, in 17.3 days; and second brood eggs (August) at 76.58° F. in 11.45
days; the average for both broods being 14.4 days (Headlee and
McCoUoch).
Larval Development. — The discussion already given of growth and
development in relation to temperature applies of course to the larval
stage as well as to all other stages of development.
Larvae of the cotton boll weevil in squares developed in 7 days at
an average mean temperature of 75° F.; the total of effective tem-
peratures being 280 degrees F. (Hunter and Hinds.)
The bollworm, or corn ear worm, developed in 21 days at an average
mean temperature of 77° F.; the total of effective temperatures being
617 degrees F. (Quaintance and Brues.)
In these experiments it was assumed, as was formerly customary,
that only temperatures above 43° F. were effective for growth; this is
known to be a mistake. A small percentage of boll worms survive
a temperature of 34° F. ; but larvae subjected to temperatures somewhat
below freezing for one to two days are killed outright.
A constant temperature of 90° F. prevents the development of the
plant louse. Aphis avence; the optimum temperature for the production
of the wingless agamic forms being about 65° F. (H. E. Ewing.)
Warmth and dryness are favorable to the development of species
of "thrips" (Thysanoptera) and of the "red spider," a well known
mite that injures plants, especially in greenhouses.
Molting. — In the walking-stick, Diapheroirtera Jemorata, a low tem-
perature lengthens, while a high temperature shortens, on an average,
the interval between molts. A low temperature has a tendency to
decrease the number of molts, while a high temperature increases the
number. (H. H. P. and H. C. Severin.)
Pupal Development. — Krogh found that the extremely simple
relation (already described) between temperature and the velocity of
embryonic development held good also for the changes taking place
during the pupal life of the meal worm, Tenehrio molitor. He says:
360 ENTOMOLOGY
(i) "The relation between the temperature and the velocity of pupal
development in Tenehrio cannot be expressed in terms of Van't Hoff's
formula, but between 18.5° and 28° the relation is algebraic and the curve
representing it is a straight line. (2) Beyond these hmits the curve
is not straight, but bends upwards at the lower temperature and down-
wards at the higher. Normal development is still possible at tempera-
tures between 15° (13.5°) and 2,^,°. (3) In the metaboHc activity of the
chrysalides of Tenehrio three stages are recognizable, corresponding
roughly to periods of disintegration of larval tissues, comparative rest
and formation of imago tissues. The metaboHsm in the tissue disin-
tegration period is practically of the same intensity as in the tissue for-
mation period. (4) The total amount of CO2 produced during the pupal
life is the same at all the temperatures examined (2i°-33°). There is
no optimum temperature with regard to metabolism. The relation be-
tween the temperature and the average CO2 production per hour
follows the same curve as that found for the velocity of development. "
Sanderson found that pupae of the meal worm, Tenehrio molitor,
failed to transform at 9° or 10° C. but transformed at 12° C; and that
pupae of the codling moth underwent little development below 55° F.
As a rule, the length of the pupal period is rapidly shortened by
increase of temperature. In Michigan, in spring, pupae of the codling
moth developed in an average of 18.4 days at an average mean tempera-
ture of 66° F. (A. G. Hammar.) The boll weevil in summer had a pupal
period of 5.1 days at an average mean temperature of 74.3° F. (Hunter
and Pierce.)
Life Cycle. — The total hfe cycle of the boll weevil, as obtained by
adding egg, larval, and pupal periods, was found to be 17.65 days, at
an average mean temperature of,77.8° F.; or an average of effective
temperaturesof 34.8 degrees; the total of effective temperatures being
614.2 degrees. As found by continuous observations on the same indi-
viduals, the life cycle was 17.7 days, with average mean temperature 76.9°
F.; average of effective temperatures 33.9 degrees, and total of effective
temperatures 600 degrees. (Hunter and Hinds.) Here, again, 43° F.
was assumed to be the " zero of development."
Acclimatization. — A few insects have become adapted to survive and
thrive under extremely high temperatures. Larvae of a fly, Stratiamys,
have been found in a hot spring in Colorado with a temperature of 69° C.
A water beetle in India was found in a warm spring at 44.4° C. Few
organisms, however, resist temperatures over 45° C. (Dr. C. B. Daven-
port.) Probably in successive generations of the ancestors of these forms
INSECT ECOLOGY 361
there were some individuals that could endure a little more heat than
the others, and gradually a resistant strain of a species was built up.
Hibernation. — Temperature manifestly bears an important relation
to hibernation, the phenomenon of passing the winter in seclusion,
usually in a quiescent or inactive condition. The stimulus leading to
hibernation is usually decreased temperature in autumn. Thus the
cotton boll weevil begins to hibernate with the decrease in mean average
temperature to about 55°. (Hinds and Yothers.) Low temperature is
not always, however, the immediate incentive to hibernation. The
codling moth larva begins to hibernate before the temperature falls
and before food fails. The woolly bear caterpillars {Isia isabella) show
great regularity in the date at which they stop feeding, under con-
ditions of high temperature, different degrees of relative humidity,
and an abundance of fresh food. (Baumberger.) Mosquitoes begin to
hibernate before cold weather sets in. Among other influences there
may be a "tendency" to hibernate in many species.
The period of hibernation is prolonged by low temperatures. The
emergence of Cecropia moths from their cocoons may be delayed for
more than one year by placing the cocoons in cold storage with the
temperature a little above the freezing point.
Warm periods during winter may arouse insects to more or less
activity. It is commonly thought by collectors that a uniformly
cold winter is more favorable to a subsequent abundance of insect life
than a winter interrupted by mild spells.
Some insects do not awaken easily from the condition of hibernation,
while others respond readily to an increase of temperature. Examples
of the latter kind are the pomace flies {Drosophila), the house fly {Musca
domeslica) and other flies, and cockroaches.
The temperature requisite to emergence varies with the species.
The boll weevil, in hibernation by the time of the first hard frost, con-
tinues to hibernate until the mean average temperature has been for
some time above 65° F. (Hunter and Hinds.) In the case of the brown-
tail moth 34° F. is the threshold above which the temperature accumu-
lates in determining the time of emergence of the caterpillars from their
winter nests. (Sanderson.)
According to J. P. Baumberger, insects hibernate as (i) adults,
when their food habits are such that oviposition can take place on the
proper food at the earliest warm weather; (2) as larvae, when protected
from the cold and thus able to continue feeding to the latest date pos-
sible; (3) as pupae or eggs, because they are nonfeeding resistant stages.
362 ENTOMOLOGY
, Many examples of adaptation in relation to winter conditions will
suggest themselves. Insects when about to hibernate seek shelter or
construct shelter, or both. They may simply crawl into existing
crevices or holes, as in the ground or in plants, under stones, logs, loose
bark, dead leaves, among stems or roots of plants, or may burrow into
the ground or into Hving or dead plants; or may miake cocoons or silken
nests or earthen cells, in which protection is afforded by surrounding air-
spaces. A curious situation for hibernation is that of back-swimmers
(Notonecta) , which have been found clustered in small cavities in thick
ice. Hibernating insects protect themselves more or less successfully
from such adverse inifluences as sudden changes of temperature, excess
of moisture or of dryness, invasion by fungi and bacteria, and from
attacks by other insects or by birds or mammals.
There are, however, many examples of unsuccessful hibernation.
Exceptionally low temperatures occasionally exterminate the boll weevil
in. certain areas, the mortality being increased by excessive rainfall.
Concerning the caterpillars of the brown-tail moth in their winter nests,
Sanderson says that where nests of average size containing 300-400
larvae were subjected to —24° F. or lower, from 72 to 100 per cent, of
the larvae were killed, but that in large nests from the same locaHty only
57 per cent, were killed; the larvae in the outer parts of the nests dying
first.
Following a period of subnormal temperatures in the state of
Washington, 1919, examinations were made of larvae of the codHng moth
under bark or burlap bands. It was found that wherever the minimum
temperature had been lower than —25° F. all larvag were killed. On
higher ground, where the minimum temperatures ranged from —20° to
— 25°, 80 to 90 per cent, of the larvae were killed. On still higher
ground, with minimum temperatures of —15° to —20°, the mortality
was approximately 70 per cent. One interesting fact noted was that
frequently, on tearing away the burlap band, one or two living larvae
would be found in the midst of a number of dead ones. It seems impos-
sible, in these cases, that the living larvae had any more protection than
the others. They must simply have had more vitality. (E. J. New-
comer.)
Distribution. — Minimum temperatures exert an important influence
in hmiting the northern distribution of insects, according to Sanderson,
from whose article on the subject the following extracts have been taken.
In New Hampshire (January, 1907) most of the hibernating caterpillars
of the brown-tail moth (excepting those in large nests) were killed off by
INSECT ECOLOGY 363
a temperature of — 24° F. and below. The northern Hmit of the San
Jose scale insect corresponds approximately with the average annual
minimum isotherm of —15° F. This species dies out in central Wis-
consin and cannot survive in Minnesota. The wide-ranging cotton
bollworm, or corn ear worm, does not winter in Minnesota and no records
of injury occur in Montana, Wyoming or the Dakotas. The harlequin
cabbage bug maintains a foothold in the latitude of Long Island,
southern Ohio and southern Illinois, but has been unable to extend
its permanent range farther north on account of being killed off by cold
during hibernation.
A blanket of snow may offset the effects of minimum temperatures,
as with the striped cucumber beetle, which hibernates in the soil, the
codling moth, which passes the winter as a caterpillar in a cocoon under
bark, the scale insects, and many other species.
Occasional periods of extremely low temperature, occurring at
long intervals, are temporary checks upon the distribution, but the
exact northern limits of distribution depend rather upon the average
minimum temperature.
Pressure
From the few observations that have been made upon the subject it
appears that insects are sensitive to variations in atmospheric pressure,
as birds and mammals, including man, are said to be. Atmospheric
pressure as correlated with humidity affects animals indirectly through
its effects on evaporation. Thus high pressure with low humidity
means increased evaporation, and vice versa.
The following extracts are from an interesting article by D. C. Par-
man on the effect of storm phenomena on insect activity.
With a rapidly falling barometer several species of flies (Muscidae)
first become nervously active and then go into a state of partial coma,
in which state they are more subject to the action of other destructive
agencies, diseases probably included. The decrease in the number of
flies is quite appreciable after a severe tropical storm.
The adults of the fly Chrysomyia macellaria apparently will not chill
and die under the effect of a rising barometer as under a lowering baro-
metric pressure.
Insects attracted to hghts are more active during high barometric
periods and especially while the barometer is rising.
Bred adult Diptera tend to emerge on periods of rising barometer.
364 ENTOMOLOGY
The hea\y emergences apparently always have been during periods of
high barometric pressure. Trappings and observations indicate that
muscoid Diptera are most abundant during long periods with slight
variations in barometric pressure, provided, of course, temperature,
humidity and rainfall are favorable.
Migration of the butterfly, Hypatus bachmani was observed during
the summer and fall of 19 16 to take place after storms, which indicates
that the flights were during high barometric pressure.
Moisture
Moisture ranks with temperature as a highly essential condition of
existence. Moisture affects terrestrial animals most vitally through
evaporation, which will be considered beyond. Here we may state
the effects of moisture without special reference to evaporation, but it
should be borne in mind that, in most of the phenomena discussed,
evaporation is an important factor.
Metabolism. — "Water plays a part in growth second in importance
to no other agent, so that in its absence growth cannot occur. As the
quantity is increased, growth is increased until an optimum is reached.
The amount imbibed does not, however, depend directly upon the
amount available, but rather upon the needs and habits of the
species." (Dr. C. B. Davenport.)
I. There is an optimum moisture for insect development. 2. This
optimum is not the same for different species. 3. The moisture which
may hasten the development of one species may retard the develop-
ment of another. (Bachmetjew.) Headlee adds that the rate of
metabolism in certain actively feeding insects with an abundant supply
of succulent food is not affected by large differences in atmospheric
moisture. He found that the green-bug, Toxoptera graminum, required
six days to pass from birth to maturity under a constant temperature of
80° F. and relative humidities of 37, 50, 70, 80 and 100 per cent. Pro-
fessor Headlee found also that, with the angoumois grain moth and the
bean weevil (i) increase in atmospheric humidity means increase in
speed of metabolism as measured by length of Ufe cycle; (2) the optimum
per cent, of atmospheric humidity is the highest which will not encour-
age a heavy growth of fungi; (3) 100 per cent, atmospheric humidity
destroys by encouraging the growth of fungi, and low atmospheric mois-
ture destroys directly — probably by the extraction of water; (4) while
the egg stage of the bean weevil, at least, is most sensitive to the effect
INSECT ECOLOGY 365
of low atmospheric humidity, other stages are unfavorably affected;
(5) low atmospheric moisture might be developed into an efficient in-
secticide for certain species of stored grain insects.
Eclosion. — Moisture frequently determines the time of eclosion,
or the emergence of an insect from the pupa. Hessian flies do not
emerge from the puparia in dry weather, but issue in abundance after
rainfall in the proper season. When bred indoors, the flies do not
emerge from dry soil, even though the temperature be favorable, but
emerge shortly when the soil is moistened.
Activity. — Wet weather lessens the activities of insects exposed to
it. There are some exceptions, however. Larvae of the midges, Itoni-
didae, are all very sensitive to the presence of moisture, to which they
react positively. Larvae of the clover seed midge emerge from the clo-
ver heads usually in damp weather and often in large numbers when the
plants are wet with rain. Even when full grown and contracted in
readiness to form the puparium, they revive and move about if mois-
tened with water.
Oviposition. — It has been found that with the house fly, when
temperatures are high or moderately high, increased humidity hastens
egg-laying. This may be partially due to the effect of humidity on
the food and breeding substances — keeping them moist and attractive.
(Bishopp, Dove, Parman.)
Mortality.— Changes in relative humidity produce striking changes
in the mortality of Drosophila, the mortality increasing with a decrease
of humidity, the optimum humidity being loo per cent. The effects
of low humidity on mortality are most marked with very youngpupae,
whose covering permits a rapid evaporation of body moisture. After
a few hours, when integumental changes making evaporation more
difficult have set in, the eft'ects of low humidity are correspondingly
decreased. (A. Elwyn.)
Hibernation. — As a preparation for hibernation, the water content
of an organism is frequently reduced; as also in seeds or spores. Thus
the Colorado potato beetle loses about 30 per cent, of its gross weight
through the loss of water, which enables it to withstand a lower freezing
point and higher temperatures than if the protoplasm were not thus
condensed. (Tower.) As Sanderson notes, the time of emergence from
hibernation is controlled by moisture conditions as well as temperature,
or independent of temperature. Tower kept potato beetles for eight-
een months at a high temperature, but with a dry atmosphere, and
they emerged as soon as normal moisture conditions were produced.
366 ■ ENTOMOLOGY
-Estivation. — In the case of the potato beetle, hibernation and (esti-
vation, or the condition of dormancy in summer, are practically the same
as regards the Hfe history of the insect, according to Tower. In the
tropics, where there is no hibernation, aestivation occurs over the dry
season. Though aestivation is associated mainly with heat, relative
humidity is also a factor, and "undoubtedly has the most important
influence upon the time of emergence of forms in aestivation during
the summer or in arid regions. (Sanderson.) During intense heat (95°
to 122° F.) the boll weevil aestivates temporarily on the ground under
protecting objects.
Drought. — ^Drought accompanies heat and affects animals and
plants through evaporation. It affects them directly, by desiccation;
or indirectly, by drying out the food plants or other food substances;
as with larvae of the boll weevil or the house fly. The range of dryness
within which insects can exist varies greatly with different species.
The chinch bug, unlike the Hessian fly, thrives in hot dry summers;
and species that inhabit arid regions are exceptionally resistant to
conditions of drought.
Precipitation. — Rainfall is direct or indirect in its influence on the
life and activities of insects. Eggs of the cotton boll worm are destroyed
in immense numbers by the mechanical force of the rain during violent
storms. The combined effects of rain, wind, and sandy particles
washed against the plants removes many eggs . (Quaintance and B rues .)
Young larvae of the bollworm feeding on corn early in the spring are
often washed down by rain and submerged for considerable periods.
Of twenty newly hatched larvae submerged for seventeen hours, all
but four survived the immersion. Larger larvae cannot stand such
long periods, but when dropped into water become stupefied after a few
minutes. Pupae could not withstand twenty-four hours' submergence
in rain water at normal summer temperatures, but at a temperature of
from 50° to 60° F. they were unharmed by from four to six days'
submergence. (Quaintance and Brues.) In the case of the cotton boll
weevil, a pupa survived an immersion of six hours; and 60 per cent, of
adults, one of fifteen hours. Ten adults were floated for one hun-
dred and twelve hours, after which only one was dead, but only two
were normal; after floating for only twenty-five hours, however, six of
the ten were normal. The floating of adults and infested squares ex-
plains the appearance of weevils in great numbers along high-water
line immediately after a flood. (Hunter and Hinds.)
Rains favor weevil increase in several ways. Frequent rains in-
INSECT ECOLOGY 367
crease the growth of the plant and lead to the production of a larger
number of squares which may become infested. Driving rains knock
off infested squares, and by softening and moistening the food hasten
the development of the larvas within. Squares which are already upon
the ground are protected during rainy weather from sunshine and dry-
ing. Rain hinders the enemies of the weevil far more than it does the
development of the weevils themselves. On the other hand, it seems
probable that as many of the hibernating weevils perish from frequent
wetting as from exposure to the cold. (Hunter and Hinds.)
Frequent heavy rains in spring reduce greatly the numbers of
immature chinch bugs.
Moisture increases the mortality of insects indirectly by favoring
the growth of parasitic fungi or bacteria. Thus, in moist weather
chinch bugs may be almost exterminated by the fungus Sporotrichum,
as described with other examples in a preceding chapter. (See
page 218.)
This chinch bug fungus will not grow in a relative humidity of 90
per cent, or less, but will remain dormant in the spore stage for an indefi-
nite period (more than eighteen months, in dryness.) The fungus can
hardly have too much moisture in a state of nature; dashing and wash-
ing rains serving merely to distribute it. (Headlee and McColloch.)
Composition
The fact that animals require oxygen for respiration, and give off
carbon dioxide, while plants utihze carbon dioxide and set free oxygen,
need only be alluded to.
The chief constituents of air are oxygen, nitrogen, carbon dioxide,
water-vapor in varying amounts, with small quantities of gaseous
ammonia and hydrogen dioxide, and extremely small amounts of argon.
The organic matters present, as bacteria, spores of fungi, pollen grains,
etc., are highly important biologically.
In atmospheric air there are very nearly three parts of nitrogen to
one part of oxygen, whether by volume or by weight; with slight varia-
tions in these proportions.
The carbon dioxide is present in relatively small quantity, about
three parts in ten thousand, the proportion varying according to the
locality and season; being greater in cities than in the country; in sum-
mer than in winter; in warm climates than in cold; in lower altitudes than
in higher; and "greatest near the ground where decomposition is taking
place."
368 entomology
Movement
The movement of air is physiologically important in affecting the
rate of evaporation from the bodies of animals. With other conditions
constant, the rate of evaporation is proportional to the strength of
the air-current.
The directive effect of currents of air (anemotropism) has been dis-
cussed (page 305). Some insects turn away from currents of air be-
cause of increased evaporation. (Shelford.)
Winds are highly effective agents in the distribution of insects.
To what has been said on this subject (page 323) these remarks may be
added.
In the case of the cotton boll weevil, "prevaihng winds frequently
cause the majority of the insects to follow one course." (Hunter and
Pierce.)
The natural spread of the gipsy moth is accomplished chiefly by
means of winds, acting on the hairy first-stage larvae. (A. F. Burgess.)
Hessian flies are often carried two miles, in an uninjured condition,
by strong winds. One female must have been carried five miles. (J. W.
McColloch.) These flies may be borne by winds with a velocity of
twenty-five miles or more per hour; mosquitoes, on the other hand,
cling to herbage near the ground during strong winds, but are conveyed
many miles by gentle breezes.
The green-bug, Toxoptera graminum, and many other plant lice
are widely distributed, as winged viviparous females, by the wind.
"If the temperature be below the point of activity for the species,
it is very clear that the velocity of the wind would have no effect what-
ever upon the diffusion of the insect. The conditions necessary, then,
for the wind to exert its greatest influence will be a decreasing food
supply for the insect under a temperature considerably above that
actually necessary for its activity, with numbers not seriously reduced
by parasites; under these conditions, many species of aphids are known
to be carried about in immense numbers by the winds." (Webster and
Phillips.)
Electricity
Electric currents have a directive effect on animals {electrotropism,
galvanotropism) but the conditions under which this effect is obtained
are artificial, and may or may not be paralleled in nature.
Atmospheric electricity, the effects of which vary with variations
INSECT ECOLOGY 369
in Other conditions of the atmosphere (Shelford), doubtless exerts
some influence on the activities of insects and other animals, but in
regard to this subject little is known.
In the hterature there are observations of the effects of electrical
storms on insects, but these effects are results of several influences
operating in combination (as temperature, moisture, pressure, light,
and wind and rain, acting mechanically) ; and possible effects of elec-
tricity alone are not distinguishable.
Evaporation
Evaporation depends upon air-temperature, pressure, relative
humidity, air-movement and, indirectly, light. The amount of evapo-
ration expresses the total effect of these factors. The evaporating power
of the air is "by far the best index of physical conditions surrounding
animals wholly or partly exposed to the atmosphere. " (Shelford.) The
rate of evaporation is directly correlated with temperature and illu-
mination, but most closely correlated with relative humidity. (Yapp.)
In the experimental study of evaporation Livingston's atmometer
is usually employed. This consists essentially of a cup of porous clay
which is filled with water, that is replaced as it evaporates, from a
reservoir of water. The amount of evaporation is easily measured by
the amount of water necessary to restore the water in the reservoir
to its original level.
Few precise studies have been made upon the effects of evaporation
on insects, though many have been made with man and other warm-
blooded animals.
Metabolism in Relation to Evaporation. — "Metabolism results
in heat, and the temperatures of the bodies of animals both warm and
cold blooded, is nearly always higher than the surrounding medium, at
least during activity. The surrounding conditions may be stated as
usually acting on metaboHsm, etc., as follows: (a) A moist cold atmos-
phere (very low evaporation) causes body temperature to fall more
rapidly than a dry cold one at the same temperature, because of the more
rapid conduction of heat. Such a fall in temperature decreases metab-
olism of cold blooded animals, and increases metabolism of warm blooded
animals within their capacity for heat regulation. In a dry cold atmos-
phere the heat loss is less pronounced because of the less rapid conduc-
tion of heat, (b) In a dry warm atmosphere (high evaporation) rapid
evaporation keeps down the peripheral temperature, and prevents death
from over-heating and destructive metabolism in cold blooded animals.
370 ENTOMOLOGY
and makes possible body temperature regulation and thus prevents
heat stroke and death in warm blooded animals. In a moist warm
atmosphere, death and heat stroke occur because of lack of evaporation
and lack of peripheral cooling in the case of warm blooded animals
even when the surrounding temperature is at or below the normal body
temperature, (c) Wind movement (which increases evaporation)
increases radiation of body heat and of heat due to insolation. It
increases evaporation and further cools the body, thus within certain
limits increasing the metabolism of warm blooded animals and de-
creasing it in cold blooded animals, (d) Decrease of pressure increases
evaporation and radiation both of which lower the temperature of
animal bodies and influence metabolism.
"Conditions which withdraw water from organisms (evaporation
as influenced by various factors) influence irritabihty, activity and
length of life history. Thus Hennings found that low humidity in-
creased insect metabolism and Sanderson found that in dry air the
optimum temperature of the growth of insects was lower than in moist
air. Factors probably operate with reference to an optimum."
(Shelford.)
Professor Headlee raised bean weevils, Bruchus oUectus, from the
eggs at a constant temperature of 80° F., but with various degrees of
atmospheric moisture, from less than i per cent, to approximately 100
per cent. The optimum relative humidity was found to lie between
80 and 89 per cent. At 89.7 and 100 fungi developed and greatly re-
duced the numbers of the insects. Comparatively few individuals
reached maturity in an atmospheric moisture of 25 per cent, and none
in one of less than i per cent.
Burger, as reported by Shelford, studied the water relations of
the meal worm, Tenebrio molitor when kept in dry air and fed on bran
which had been dried at 105° C. He believed that the animals were in
essentially absolute dryness. Here they lived for weeks, but lost
weight. He found, however, that the per cent, of water in the animals
remained practically the same until after death and came to the conclu-
sion that the insect larvae could not use their food to produce water and
so the living substance itself was used. No doubt the food taken pro-
duced water but this was not sufficient in quantity. The most important
fact brought out was that the per cent, of water remained about the
same in spite of the extreme dryness and rapid loss of moisture.
Reactions." — Professor Shelford, who studied experimentally the
behavior of various animals under different rates of evaporation, found
INSECT ECOLOGY 37 I
that in dry air (evaporation 0.06 cc. per hour) running beetles of the
genus Pterostichus were very sensitive, exhibiting a preference for
moist air. Digger wasps, Microhemhex, were sHghtly positive to dry
air, their chief reaction being digging, which took place in medium and
moist air but not in the dry. A tiger beetle, Cicindela, gave a nega-
tive reaction to air evaporating 3.6 cc. per hour, and a positive reaction
to air evaporating 1.56 cc. per hour.
Shelford studied also the influence of rapidly flowing and of warm
air in increasing evaporation. All the animals that he studied could be
killed by loss of water, when other conditions remained favorable to
their existence. The smaller animals died from loss of water much
more quickly than the larger, the surface being greater in proportion to
the volume in the smaller animals. The animals died after a smaller
amount of evaporation when the rate was slow than when it was more
rapid. The most remarkable fact brought out was that the animals died
more quickly from evaporation due to rapid movement of air than due
to dryness.
With a total evaporation of 31.0 cc. in a dry atmosphere Pterostichus
died in twenty-two hours.
The Pterostichus referred to came from under leaves on the ground
in a dense forest — a moist habitat; and Microhemhex is a resident of
dry open sand areas. '
Hatching. — With fertile eggs of plant lice {Aphis avence and A.
pomi) air of high moisture content is more favorable to hatching than
air having a lower moisture content. The moisture content of the air
influences the evaporation from the eggs, determines the percentage of
hatching, and probably influences the rate of splitting of the outer
layer of the egg shell. (A. Peterson.)
Nymphs of walking-sticks, Phasmidae, frequently fail to extract
themselves from the egg shell, owing to dryness at the time of hatching.
Most of them succeed in escaping, however, if supplied with moisture.
In this instance evaporation has the mechanical effect of causing the
appendages or the abdomen to adhere to the amniotic membrane. (H.
P. and H. C. Severin.)
Life Cycle. — The length of the life cycle is often influenced greatly
by evaporation as determined by temperature and relative humidity.
With the Hessian fly, high temperature and low humidity lengthen the
cycle. In a dry atmosphere the eggs shrivel; in periods of drought
most of the puparia dry out and die. High temperature with high
humidity, however, does not retard the development, and is not fatal.
372 ENTOMOLOGY
Low temperatures lengthen the cycle and may be fatal to prepupal
stages. Low humidity also increases the length of the cycle, and if
extreme is fatal in all stages of development. (Headlee.)
Eclosion. — Every one who has had experience in raising moths
from pupse knows that the pupae must have a certain amount of
moisture or they will dry out and die. Out of doors the rainfall sup-
plies the requisite moisture, but even there pupae may succumb to too
much or too little moisture.
Moths and butterflies upon emerging from the pupa can not expand
their wings if the air is too dry, on account of the rapid evaporation of
moisture from the wings. Indoors the moisture must be supplied if
necessary. It has often been observed that moths emerge from cocoons
in greater numbers on damp days. In dry weather many insects emerge
at night, when the relative humidity is higher than in the daytime.
This incidentally protects the helpless. insect from its diurnal enemies.
Adaptations. — Many thin-skinned larvae, as those of the house fly
and the plum curculio, that live in a moist environment of decaying
substance, die quickly if subjected to a dry atmosphere, when the tem-
perature alone is not sufificiently high to kill them. On the other hand,
larvae with a thick integument, like the meal worm, resist evaporation
more successfully.
An immense number of dipterous larvae, those of the Hessian fly
and the house fly, for example, when full grown retain the larval skin
instead of shedding it; this skin drying and hardening to form a pupa-
rium, which retards evaporation from the developing pupa within. An
unusually hot dry summer will, however, kill most of the puparia of
the Hessian fly, excepting such as may be protected by their depth in
the soil.
Some of our large silkworms smear the inner surface of the cocoon
with a waterproof gum or varnish which undoubtedly prevents the un-
due esca;pe of water from the enclosed pupa.
Larvae that burrow into the ground (for example many caterpillars
and maggots, white grubs, larvae of the plum curculio, Colorado potato
beetle, and numerous others) and make earthen cells in which to pupate,
secure thereby protection from evaporation as well as from other
influences. Larvae of the late fall brood of the bollworm (corn ear
worm) dig much deeper than those pupating earlier in the season.
(Quaintance and Brues.)
The beetles of the subfamily Eleodinae (Tenebrionidae) that are
characteristic of arid and semi-arid regions, have a thick integument and
INSECT ECOLOGY 373
are quite at home in the desert. The integument is possibly no thicker
than in other tenebrionids, but having a thick skin to begin with, these
forms have found a suitable environment and have thrived in arid
places.
3. Food Relations
As regards its kind and quantity, food is, needless to say, a most
important condition of existence. Examples of food habits have been
given (page 212); here should be mentioned some of the more essential
facts concerning food as an ecological factor.
Classification of Food Habits. — According to the nature of their
food, most insects may be classified as follows: pantophagous (omnivo-
rous); phytophagous (plant-eating, referring usually to the flowering
plants); monophagous (with a single food plant); oligophagous (with
several definitely fixed food plants) ; polyphagous (feeding indiscrimi-
nately on many plants); sarcophagous (carnivorous); har pacta phagous
(predatory) ; entomophagous (parasitic on insects) ; saprophagous (feed-
ing on decaying substances) ; necrophagous (feeding on dead animals) ;
coprophagous (eating excrementitious material) ; mycetophagous (feeding
on fungi) ; microphagous (on micro-organisms, as bacteria, yeasts, etc.) .
Not all these categories will be considered here, but a few of them
need special mention.
Microphaga. — The pomace flies (Drosophila) famous as subjects of
investigation by geneticists, feed naturally in fermenting fruits, where
they find nourishment, not in the products of fermentation, but chiefly
in the yeasts that cause the fermentation. On sterilized glucose-agar
the larvae cannot grow unless yeast is added; and a medium of yeast
nucleo-protein, sugars and inorganic salts is a complete food for this
insect. (Loeb and Northrop, Baumberger.)
Sarcophaga. — Dipterous larvae that normally feed on decaying
animal tissue were raised from eggs to adults on a diet of banana and
yeast-agar, by Baumberger, who says that we must consider the
probabiUty that all decaying or fermenting substrata are merely the
media on which fungous or bacterial food of insects is growing.
Coprophaga. — ^Larvae of the house fly were raised on bran mash
containing a heavy growth of molds. Sections through these larvae
showed a complete absence of all material except bacteria, fungous
spores, and yeast cells in the digestive tract. It appears probable that
the larvae feed on micro-organisms, and are associated with them in the
same manner as that of Drosophila and yeasts. (Baumberger.)
374 ENTOMOLOGY
Mycetophaga. — Many, though not all, of the fungus flies (Myceto-
philidae) feed on fungi. Larvae of a species of Sciara that feeds in woody
tissue were found to contain in the digestive tract fungous mycelia
along with considerable woody material. Larvae of the same species
were reared on a medium of bran-agar, which they soon infected with
molds, upon which they were subsequently observed to feed. The
wood is merely the substratum in which the food material develops.
(Baumberger.)
The ambrosia beetles, of which there are many species, make their
tunnels in damp wood of weak or dead trees. Their food is not wood,
however, but a fungous growth which develops rapidly on the walls of
the galleries — so rapidly often as to choke the galleries and kill their
inmates. The fungus begins its growth on a bed of chips which the
female prepares, and on which she lays eggs. The fresh tender growth
of the fungus is food for both larvae and beetles, but only the latter can
eat the older growth. "Different species of fungi are associated with
different species of beetles, and these associations are constant for the
same species in spite of changes of host plants." (Baumberger.)
In connection with this subject the elaborate fungus-gardens of
leaf-cutting ants and of termites should be recalled (page 295).
Selection of Food. — Insects find food for themselves or for their
future larvae by means of the senses of (i) smell, the most widespread
method; (2) taste, as with butterflies, pomace flies, flesh flies and other
forms that feed as adults; (3) vision, as with dragon flies, which after
capturing their prey test it, however, and reject portions unsuitable as
food; also bees, which can discriminate between flowers of different
colors.
Brues adds, in his paper on this subject, that the selection of food
plants by Lepidoptera depends also on (i) "Some attribute of the plant,
perhaps an odor but far less pronounced to our own senses than those
mentioned above. Species restricted to plants like Leguminosae or
Violaceae may be considered in this category. Undoubtedly there is
some attribute of such plants which insects can recognize in a general
way and not as a specific characteristic of some single plant species or
genus. (2) A similarity in the immediate environment or general form
of the food plant. The effect of something of this sort is seen particu-
larly in oligophagous and also polyphagous caterpillars feeding mainly
on trees or shrubs, such as the gipsy moth, Cecropia moth, etc., and those
of certain species like some of the Arctiid moths that feed upon a great
variety of low plants. (3) Apparently chance associations that have
INSECT ECOLOGY 375
become fixed, whereby diverse plants are utilized by oligophagous
species."
The selection of food by means of its odor is simply a case of positive
chemotropism (see page 302), a blind reaction to a chemical substance.
Pomace flies, which feed on and lay their eggs in fermenting fruits, are
positively chemotropic to weak percentages of certain alcohols and
acetic acid, which are products of fermentation. House flies are stimu-
lated to oviposition by ammonium carbonate, with its odor like that of
manure. The cabbage butterfly is induced to lay eggs by mustard
oils, which occur naturally in its usual food plants, Cruciferae.
Growth. — Other things equal, the length of the larval stage depends
upon the kind, condition, and amount of food. With the house fly, it
is primarily temperature and moisture that determine the rate of devel-
opment; but with an average temperature of about 21° C, the maggots
develop in. horse manure in fourteen to twenty days, and on a diet of
bananas, in twenty-seven days. At the same temperature, the rate of
development is directly proportional to the condition of the food as
regards moisture. Dry conditions may retard development five or six
weeks, tend to produce flies of subnormal size, or may be fatal. (C. G.
Hewitt.)
If the mother insect lays her eggs in a considerable supply of food
substance, as happens usually in the case of the house fly, pomace fly,
carrion beetles, dung beetles, and many other insects, the development
of the larva is assured, so far as the amount of food is concerned. The
quantity of food present becomes important, however, for insects that
are restricted to one kind of food plant, or to a food of low nutritive
value. The nutritive content of wood is small, and wood-boring cater-
pillars and grubs frequently require long periods for their growth, even
several years (Cerambycid^) ; though less time is needed if the larvae,
like those of the peach tree borers and the flat-headed apple borer,
feed largely on the inner bark, which is more nutritive than the
wood.
Size. — Under-nourished larvae produce small adults, as might be
expected. The size of boll weevils depends upon the abundance of the
food supply and also upon the nature of the food. The smallest weevils
develop from squares which are very small, and which fall very soon
after the egg is deposited ; the largest, from bolls which grow to maturity.
In bolls the food supply is most abundant, and the period of larval
development is several times as long as it is in squares. (Hunter and
Pierce.)
376 ENTOMOLOGY
Reproduction.^ — It goes without saying that constant feeding is
necessary in the case of long-Uved proHfic females, such as queen bees,
ants, or termites.
With plant lice, it has long been known that the drying up of the
food plant causes the appearance of large numbers of winged, or migrant
females. In experiments with the pea louse, Macrosiphum pisi, it
was found that the subjection of parthenogenetic (reproducing without
fertilization) females to periods of partial starvation induced the produc-
tion of winged offspring from the wingless mothers. These winged
young would otherwise have been wingless, as check experiments
showed. (L. H. Gregory.)
In regard to the relation of food to the production of the males and
oviparous (egg-laying) females of plant lice, not much seems to be
definitely known.
Fecundity. — The kind and amount of food influence fecundity. If
female boll weevils are fed on leaves alone, eggs do not develop; while
a diet of squares leads to the development of eggs in about four days.
More eggs are laid when squares are abundant than when they are few.
(Hunter and Pierce.)
Guyenot found that pomace flies {Drosophila) reared from aseptic
larvae on sterile potato (without yeast) did not produce offspring. The
flies themselves, if fed on potato alone, were much less prolific than when
fed on potato and yeast.
Oviposition. — With many adult insects feeding is not necessary for
oviposition; in fact the mouth parts are often rudimentary, as in some
of the moths. Such insects owe their activity to the presence of a
supply of food stored up by the larva. Other insects, however, must
feed in order to lay. eggs; the queen honey bee, for example.
Adults of Pteromalus puparum, a parasite of the cabbage butterfly,
Pieris rapee, if kept without food for three days, attempt to oviposit
but are physically unable to do so. If then fed, however, with honey-
water or with blood from punctured chrysalides (their natural food),
they succeed in drilling into the chrysalides of their hosts. When
supplied with fresh pupae one of these females may feed and lay eggs
for three weeks; and if given honey-water also, for two months.
(S. B. Doten.)
Sex-determination.— One of the most plausible of the theories of
sex-determination has been that high nutrition produces females and low
nutrition, males. In raising moths or butterflies from caterpillars
males and females occur in about equal numbers, as a rule. If, however.
INSECT ECOLOGY 377
the caterpillars are almost starved, some will die, and there will result
many more male adults than female. Dr. C. V. Riley explained this
long ago, by pointing out the fact that female caterpillars require a
longer time for growth than males (having sometimes one more molt
than the males); so that conditions of starvation would kill chiefly
female caterpillars, that had not completed their growth, and affect
male caterpillars less. T. H. Morgan, in a discussion of the subject,
adopts this view, and points out the fact that the sex of the caterpillar
is determined before the egg is laid; furthermore, that an excess of food
does not cause an excess of females.
Longevity. — The duration of life is evidently related to food.
Insects cannot live long, if active, without food; and activity is corre-
lated with the amount of food utilized.
Females live longer than males, with some exceptions, particularly
if they have not laid their eggs, and frequently, possess an ample supply
of reserve food accumulated by the larva, as in the case of many moths,
particularly such as do not themselves feed as adults (silkworm moth) .
With cotton boll weevils after emergence from hibernation, unfed
beetles of both sexes were found to live ten days, and fed beetles,
twenty-five days. (Hinds and Yothers.)
A queen honey bee, constantly fed with highly nutritious food,
may live more than four years; a queen ant, fifteen years (one instance).
On the other hand, the Hessian fly, which does not feed and has
little reserve nutriment, lives only from one day (males) to four days
(females) .
A remarkable instance of longevity under starvation conditions is
given by J. E. Wodsedalek. Finding that larvae of the common museum
beetle, Trogoderma tarsale, would live a long time without food, molting
meanwhile but not eating the cast skins, he tested their longevity by
keeping them individually in glass vials without food. The larvae
gradually decreased in size to almost their length at hatching, but were
surprisingly tenacious of Hfe. Newly hatched larvae that had never
eaten lived four months without food; quarter-grown larvae, fourteen
months; half -grown larvae, three years; three-quarters-grown larvae,
four years; and full grown individuals, from four years to five years,
one month and twenty-nine days (one larva). If stunted specimens
were given food they began to grow again, and could again be reduced
in size by a second period of starvation. By alternate periods of feasting
and fasting, larvae were three times brought to their maximum size
and three times reduced to the minimum size.
378 ENTOMOLOGY
Hibernation. — Food is of minor importance as an incentive to hiber-
nation. Codling moth caterpillars, woolly bears {Isia isahella) and
many other insects enter hibernation before there is any failure of the
food supply.
Insects which feed on evergreen trees are not as rhythmical in
their hibernation as those which feed on deciduous trees. (Pictet,
Baumberger.)
Some larvae are full-fed upon entering hibernation (codHng moth) ;
while others are not (brown- tail moth). Emergence from hibernation
depends immediately upon temperature, but it is possible that hunger
also is a stimulus to the renewal of activity.
As metabolism is at its minimum in hibernating insects, their food
requirement is similarly small.
Coloration. — Food, as regards kind and condition, often affects
coloration, particularly pigmental coloration (see page 176).
In the cotton boll weevil the color becomes darker with age; conse-
quently, hibernated individuals are the darkest found; but food also
influences the color. The smaller the size of the weevil, the darker
brown is its color; the largest weevils are light yellowish brown. The
principal reason for the variation, in the opinion of Dr. W. E. Hinds,
lies in the degree of development of the minute, hair-like scales, which
are much more prominently developed in the large than in the small
specimens, although the color of old specimens is often changed by, the
abrasion of the scales. These scales are yellow in color, while the ground
color of the integument bearing them is a dark brown or reddish brown.
The development of the scales appears to take place mostly after the
adult weevils have become quite dark in color, but before the chitin
becomes fully hardened. They seem, therefore, to be, to a certain
extent, an aftergrowth which depends upon the surplus food supply
remaining after the development of the essential parts of the weevil
structure. (Hunter and Pierce.)
Food Relations in General. — A phytophagous species which is
limited to one species of food plant frequently dies out in a locality
from having consumed or fatally weakened all its food plants (the but-
terfly L. philenor, on Aristolochia, in the North).
Evidently, a species which has many kinds of food plants has an
advantage (gipsy moth, grasshoppers, army worm, etc.).
The quantity of food present becomes important for an insect that
is restricted to a single species of plant. It may be a plant that is
INSECT ECOLOGY 379
always abundant, like the pawpaw, to which the Ajax butterfly is
confined; or it may not be.
In a state of nature, if food plants of one species are scattered among
other plants, their insect enemies do not become injurious; but in a
state of nature, if many plants of one species grow together, insects may
injure them (in forests, for example). Where man grows one kind of
plant over a large area, insect enemies flourish (Hessian fly, chinch bug,
cotton boll weevil, codling moth, etc.).
The same relations exist between parasites or predators and their
hosts. A parasitic species of insect that is limited to one species of host
will die if it destroys all the individuals of the host species. The
successful parasites (as Ichneumonidae, Chalcididae, and Braconidai)
are those that have available immense numbers of a single species of
host, or a large number of species as hosts.
Most predaceous insects, however, feed indifferently on almost any
species of insects that they can overcome, and of ten do not limit them-
selves to insects for food; therefore their numbers are not affected by the
absence of this or that species of possible victim.
These food relations form a most important factor in the interactions
of organisms, the subject next to be considered.
4. BiOTic Conditions
The animals and plants of a region form a vast complex, in which
every organism affects every other, directly or indirectly, and is in turn
affected by all the others. Furthermore, all the organisms are influenced
by their environment, and in turn affect the character of the environ-
ment itself more or less. All the organisms are bound up with one
another in an intricate network of interactions which the mind can only
partially comprehend.
Interactions. — As a familiar illustration of these interactions, take
the case of any common plant louse and the extensive society, or conso-
cies, which it dominates.
To begin with, the numbers of aphids depend greatly upon inorganic
influences, as heat or cold, dryness or moisture; evaporation being
important. Aphids are often blown off their plants, or washed off by
rains, and killed mechanically. When they are abundant, many are
squeezed to death between branches that are blown against each other.
Bacteria and fungi destroy the lice. The fungus, Empusa aphidis, is
the most important enemy, for in damp weather it can almost extermi-
38o
ENTOMOLOGY
nate plant lice locally. Weather conditions may render the plants
unfit for food, or may prevent the eggs from hatching. In short,
aphids are affected for good or ill by all the influences that act upon
their food plants.
Enemies are abundant. Many kinds of spiders and a few kinds of
mites kill the Hce. The EngHsh sparrow eats the pea louse voraciously,
and the chickadee in winter consumes enormous numbers of aphid eggs.
Most of the enemies are, however, other insects. Here are lists of the
insects known to affect, directly or indirectly, the common pea louse,
or clover louse, Macrosiphum pisi.
Predators^
CoccinellidcR (lady beetles)
Ceratomegilla fuscilabris
Hippodamia tredecimpunctata
Hippodamia parenthesis
Hippodamia glacialis
Hippodamia convergens
Coccinella novemnotata
Cycloneda sanguinea
Adalia bipunctata
Chilocorus bivulnerus
SyrphidcB (flower flies)
Ocyptamus fuscipennis
Platychirus quadratus
Syrphus americanus
Syrphus ribesii
Allograpta obliqua
Mesogramma marginata
Mesogramma polita
Sphaerophoria cylindrica
ChrysopidcB (lace-wings)
Chrysopa oculata
Chrysopa rufilabris
Chrysopa plorabunda
Gryllida (tree-crickets)
(Ecanthus confluens
Pentalomidce (stink bugs)
Podisus maculiventris
Euschistus variolarius
Anthocoridce. (flower bugs)
Triphleps insidiosus
CantharidcB (cantharids)
Podabrus rugulosus
Podabrus tomentosus
Ilonididce (gall gnats)
Aphidoletes meridionalis
IchneumonidcB (ichneumons)
Praon simulans
Trioxys cerasaphis
Aphidius fletcheri
Parasites
Aphidius washingtonensis
Aphidius rosse
Miscogasteridce (miscogasterids)
Megorismus fletcheri
The species of the preceding list feed directly on the pea louse.
Those of the following list affect the louse indirectly, by feeding on the
preceding species or on one another.
1 Additional details in regard to all these insects will be found in Bull. 111. Agr. Exp.
Sta., No. 134, and Bull. U. S. Dept. Agr., No. 276.
INSECT ECOLOGY 38 I
Affecting M. pisi Indirectly
Braconida (braconids)
Perilitiis americanus, parasitic on the beetles, Ceralomegilla fuscilahris and Coccinella
novemnotata.
Bassus Icetotorius, a parasite bred from larvjc and pupa; of Allograpla obliqua and five
other species of Syrphidce.
Figitidce (figitids)
Sohnaspis hyalinus, a parasite from larvae of M esogramma polila.
Pteromalidcc (pteromalids)
Pachynenron syrphi, a parasite of Bassus Icetotorius.
EncyrtidcB (encyrtids)
Encyrlus mesograptcB, a parasite from larvae of M esogramma polita.
Chalcididce (chalcids)
Isocratus vulgaris, a parasite of Bassus Icetotorius.
Proctotry pidce (proctotrypids)
Telenomus podisi, a parasite of the eggs of Podisus and Euschislus.
A few examples will illustrate the intricacy of the interrelations of
these insects that are dominated by Macrosiphum pisi.
M. pisi is preyed upon by lady beetles, the pupae of which are sucked
by the stink bugs, the eggs of which are parasitized by a proctotrypid.
M. pisi is food for larvae of flower flies, the larvae and pupae of which
are parasitized by a braconid, which is itself parasitized by a pteromahd
and a chalcid.
M. pisi is destroyed by larvae of flower flies, the larvae of which are
attacked by stink bugs, while the adults are eaten by robber flies, toads,
and various birds, as the kingbird, flicker andphoebe.
Thus forty species of insects are known to be vitally concerned with
the pea louse. There should be added the mite, Rhyncholophus parvus,
which feeds on the louse.
The writer has found more than two hundred species of insects in a
field of red clover. All these have some influence on the pea louse
(clover louse) and on each other; though the influence is often remote in
its effects and practically insignificant. The scavenger insects on the
ground, and collembolans etc., in the soil, feeding on organic matter,
affect the texture and composition of the soil and consequently the
plant. Without considering earthworms, moles, mice, birds and many
other animal factors that might be thought of, we shall mention insects
orfly. The bees that pollenize the flowers, and the various insects that
destroy the roots, stems, leaves or flowers, all affect indirectly the louse.
As illustrating interactions, though it is of no practical consequence,
we may say that the yield of clover seed depends slightly upon the struc-
ture of the milkweed flower; for flower flies whose larvae destroy plant
382 ENTOMOLOGY
lice are sometimes fatally entangled in the flowers of milkweed. We
might even go farther, and implicate all the factors that control milk-
weed; and so on indefinitely. Such speculation is not altogether profit-
less, if one bears in mind the fact that only the more immediate
influences are of any practical importance, and that the effect of one
factor may be increased, diminished, or neutralized by that of another.
Every one of the insects or other animals that affect the clover
louse directly or indirectly, is itself the center of a little world of inter-
actions. Though we cannot follow all these interactions, their total
effect at any given time is expressed by the existing number of individ-
uals of each of the species involved; which measures also the success of
each species from its own point of view, so to speak.
Equilibrium.— It is not surprising, then, that species fluctuate in num-
ber of individuals. The presence or absence, or increase or decrease,
of one influence may affect many other factors, and disturb preexist-
ing relations. This is seen in the case of the rapid multiplication of
the gipsy moth and the San Jose scale insect, when introduced into
this country without their natural enemies.
Evidently there is actually no such thing as a "balance of nature,"
a true equilibrium; on the contrary there is continual fluctuation
within wider or narrower limits. The so-called equilibrium is simply
a condition of relatively small fluctuation. Under conditions of
nature, animals and plants approximate a condition of stability, or
fluctuation within comparatively narrow limits, to the benefit of all
concerned. Under artificial conditions, however, as when man grows
one kind of plant over a large area, the insects of the plant multiply
rapidly. Man is able to remedy such disturbances of the "order of
nature" in proportion to his knowledge of the factors concerned, espe-
cially of their relative importance. He has unwisely introduced the
English sparrow to subdue caterpillars; but has wisely imported and
propagated the native enemies of the fluted scale, the gipsy moth, and
other pests.
II. Conditions or Aquatic Existence
The fundamental physiological requirements are the same for
aquatic as for terrestrial animals, but these conditions are often met in
different ways in the two groups. Though insects may broadly be
divided into these two groups, there are many kinds whose environment
is intermediate between water and land, and many forms are aquatic
in their immature stages and terrestrial as adults.
INSECT ECOLOGY 383
I. Chemical Conditions
Animals cannot exist in water that does not contain certain
gases and chemical compounds in solution.
Gases. — Oxygen is a necessity, and most aquatic animals select
water with a high oxygen content. In air dissolved in water the pro-
portion of oxygen to nitrogen is much larger than it is in atmospheric
air ; because oxygen is more soluble in water than nitrogen. The oxygen
content of the water is more variable than that of the atmosphere.
The importance of the oxygen factor is indicated by the many elaborate
adaptations for respiration displayed by aquatic insects.
Carbon dioxide given off by animals during respiration, acts in
small quantities as a stimulation to respiration, and in large amounts
as a narcotic capable of fatal effects. Aquatic animals react nega-
tively to even a small increase of carbon dioxide. This is due to the
increase in hydrogen-ion concentration which it causes. Since a large
amount of dissolved carbon dioxide is commonly accompanied by a
low oxygen content as well as other important factors, the hydrogen-ion
concentration of waters of low alkalinity is probably the best single
index of the suitability of the water for animals. (Shelf ord.)
"Nitrogen has little effect upon animals except when present in
excess." (Shelford.)
"Oxygen and nitrogen go into solution from the atmosphere and
oxygen is also produced by green plants. The other gases are produced
chiefly by organisms as excretory and decomposition products."
(Shelford.)
Chemical Compounds.^ — Carbonates, sulphates, and chlorides of
magnesium, calcium, and sodium, and salts of potassium, iron, and
silicon are practically always present in solution in water, and their
presence in definite proportions is essential to the life of the animals.
(Shelford.) Sodium chloride, or common salt, is unfavorable to insect
life. Almost no insects live in the ocean (see p. 170). In fact, if an
insect larva be taken from a brook and put in a brackish pool it will
actually lose water through its skin ; it will partly dry up. (F. E. Lutz.)
Flies of the genus Ephydra are, however exceptional in this respect.
Two species of these "salt-flies" are abundant in Great Salt Lake, the
salinity of which is greater than that of the ocean. The flies and pupa-
ria sometimes occur in inconceivable numbers, the latter forming large
brown patches on the water or windrows on the shore. The larvae,
which feed on an alga, are active even when the water evaporates
384 ENTOMOLOGY ^
down until covered with a crust of salt. (J. M. Aldrich.) Not a few
insects live in brackish water, however; some of them occurring also
in fresh water; as the nymphs of certain dragon flies, which inhabit also
salt, sulphurous, or slightly alkaline ponds in the West. (R. C. Osburn.)
A few Hemiptera of fresh- water occur also in brackish water or in water
strongly impregnated with various mineral salts. (H. G. Barber.)
Several species of mosquitoes confine themselves for breeding purposes
to salt marshes, where A'edes sollicitans is always the most abundant
and is found in practically all the temporary pools uninhabited by fish.
(J. A. Grossbeck.)
Larvae of the malaria mosquitoes {Anopheles) also develop in
brackish water. The salt marsh mosquito {Aedes sollicitans) was
found to develop in water so strongly polluted with acid waste from a
"guano factory" that all other animal life appeared to be extinct.
(S. F. Hildebrand.)
Water containing certain acids, as the humic acids of peat bogs, is
deleterious to insect life.
.2. Physical Conditions
Circtilation. — "The distribution of dissolved salts and gases is
dependent upon the circulation of the water, as their diffusion is too
slow to keep them evenly distributed. The circulation of water in
streams is probably such as to keep all dissolved gases and salts about
equally distributed. The water of streams has been found to be
supersaturated with oxygen. Oxygen is taken up by the water near the
surface. Nitrogen and carbon dioxide are produced especially near the
bottom, and if the water did not circulate they would be too abundant
in some places and deficient in others for animals to Uve. " (Shelf ord.)
The flowing or splashing of water increases the oxygen content.
Larvae such as the hellgrammite, those of black-flies (Simulium) and
of some caddis flies (as Hydropsyche) require well-aerated water, and
are found always in moving water, often in strong currents. They
occur in flowing water not primarily on account of its greater oxygen
content, however, but because, as Shelford has shown, such animals
orient themselves toward a strong current of water (positive rheotaxis)
and move against the current. Furthermore, they are positively thig-
motactic and show a strong preference for hard surfaces, as those of
large stones; with an avoidance of sand; the members of a rapids
community differing from those of a pool community in this respect.
INSECT ECOLOGY 385
Hydropsyche reacts positively to the direction of light, though indifferent
to its intensity; but some other members of the rapids community, as
hellgrammites and burrowing caddis worms, avoid light.
"Current is an important factor of aquatic environments which
finds its terrestrial counterpart in winds. That it is a very important
factor is shown by the numerous devices aquatic insects have to keep
their position, and it varies from nothing in puddles to the rush of
Niagara." (F.E.Lutz.) Larvae of the black-flies are fastened to stones
or other objects; some caddis worms anchor their cases securely; beetles
of the family Elmidae cling with their claws tightly to submerged objects.
With caddis flies of the family Hydropsychidae, which live in swift
streams, the instantaneous emergence of the adult as soon as the pupa
reaches the surface prevents the fly from being swept away. (C. E.
Sleight.)
Temperature. — Temperature is of great indirect importance in the
control of the distribution of life in water. (Shelford.) It is "more
constant in aquatic environments than in terrestrial, although it is
somewhat variable from place to place and month to month. In the
summer, a spring hole is cooler than a rainwater puddle and the opposite
is apt to be true in the winter. In general, a running stream is apt to
be cooler in summer than a stagnant one. In the spring a deep pond is
generally cooler than a shallow one, and the opposite is true in the
autumn. But aquatic insects are never subject to the sharp daily
fluctuations of temperature that most of their terrestrial relatives must
bear, and even the annual range of temperature variations is slight. "
(F. E. Lutz.) Such differences as there are have, however, an influence
on aquatic life. Temperature affects activities of various kinds, as
locomotion and oviposition; may determine the length of the egg-
period; or may act in other ways.
Light. — Light controls distribution and activities. Its intensity
decreases rapidly, particularly that of the orange and red rays, with the
depth of the water. Aquatic insects, like terrestrial, react either posi-
tively or negatively to the directive action of light {phototropism, p.
306). Some of them frequent shaded or dark places, while others, as
the whirHgig-beetles {Gyrinidce) and the water-striders {Gerrida) are
at home on the surface of the water in the strongest sunlight.
Pressure. — Pressure in water increases with depth, at the rate of
about one atmosphere for each thirty-three feet (Shelford) . Its effects
on aquatic insects are for the most part indirect; the pressure affecting
other conditions of existence.
25
386 ENTOMOLOGY
Depth. — Depth is mostly important indirectly, on account of its
influence on other conditions, such as circulation, temperature, light,
and pressure; but is in itself a determining condition in some instances.
Thus such larvae of horse-flies (Tabanidae) as have a posterior res-
piratory tube bearing the spiracles must have shallow water, where the
spiracles can be raised to the surface; though sometimes these larvae
are found in moist earth where there is no standing water. (R. C.
Osburn.)
Bottom. — "The character of materials and topography of the
bottom are very important to animals living on the bottom, but it has
its effect also on free swimming animals as a determining factor in the
amount of sediment. The kind of bottom is important because many
animals are dependent upon sohd objects for attachment and are absent
from bottoms made up of fine materials. Others must burrow into
mud or creep on sand and gravel. " (Shelford.)
Most Dytiscidae prefer clean live water, being averse to very muddy
bottoms. (J. D. Sherman.) On the other hand, nymphs of various dra-
gon flies bury themselves in the mud. Some of the caddis worms prefer
a clear sandy bottom; others, a bottom with slime, or one with sticks,
dead leaves or other debris.
Vegetation. — It goes without saying that vegetation, in its amount
and kind, is extremely important as a condition of aquatic existence.
The green plants give off oxygen. Plants are used for shelter, escape
from enemies, as places in which to wait for the prey (dragon fly
nymphs, Zaitha), as surfaces for locomotion (non-swimming larvae
of diving beetles, whirligig beetles and others) , especially as a means of
reaching the surface for air or for the transformation (dragonfly nymphs,
etc.). Eggs may be laid on the plants (electric light bugs, back-swim-
mers. May flies, caddis flies, etc.) or inserted into plant tissues (diving
beetles, water scorpions).
3. Food Conditions
The small beetles of the family HalipHdae are said to feed on algae.
The water-scavenger beetles (Hydrophilidae) feed mostly on decaying
vegetable matter, but are sometimes carnivorous, and some ofjthe
adults will eat green vegetation. The diving beetles (Dytiscidae)
are carnivorous; the whirhgig beetles (Gyrinidae) feed on small insects
found on the surface of the water. The water-striders (Gerridae)
capture disabled or living insects for food; the water boatmen (Corix-
INSECT ECOLOGY 387
idae) are predaceous. Nymphs of dragon flies are predaceous, catching
other insects by means of their peculiar extensile lower lip, and even
young fishes, tadpoles and smaller nymphs of their own kind. (R. C.
Osburn.) Most caddis worms are plant-eating, but some are insectiv-
orous, as Hydropsyche, which catches its victims in the nets that it
spreads in swift currents. May fly nymphs are carnivorous, or feed on
plants or mud. Additional examples of food habits are given on p. 165.
4. BiOTic Conditions
Aquatic animals and plants, like terrestrial, form a vast complex of
organisms that interact upon one another in innumerable ways and are
acted upon by the environment; but the interactions are different to the
extent that the aquatic environment differs from the terrestrial. As
a whole, the physical and chemical conditions of existence are more
uniform in water th^n on land. Furthermore, the number of species
concerned is fewer; thus aquatic insects form only 3 per cent, of all
insects. As regards food supply, the truism that its diminution lessens
the numbers of the animals dependent upon it, applies of course, as with
terrestrial forms. Aquatic insects are, however, much less specialized
than terrestrial as regards food habits. Thus the plant-eating species
are seldom limited to one species of plant, therefore can always find
food, even though there are fewer species of aquatic plants than of
terrestrial. The great majority of aquatic insects are, however, carniv-
orous, and many are omnivorous, and rarely suffer from lack of food.
Though the predaceous habit is highly developed among aquatic
insects, the parasitic habit has developed almost entirely among terres-
trial forms; and aquatic insects, while actually in the water, are practi-
cally free from the attacks of parasitic insects.
On the whole, the interrelations of aquatic forms, though incon-
ceivably complex, are less extensive than those of terrestrial species.
The so-called equilibrium or "balance of nature" is maintained,,
which is, as on land, a condition of continual fluctuation within rela-
tively narrow limits; with a smaller range of fluctuation in the aquatic
environment.
Ill . Environmental Factors in General
The important factors of the environment have been considered
individually. In nature they do not operate singly, however, and by
388 ENTOMOLOGY
simple observation, unaided by experimentation, one cannot disen-
tangle the effects of one factor from those of others acting with it.
The environment is a complex of many interdependent factors.
The factors control one another, but those that are more immediate
in their operation are controlled by the larger influences of physiography
and vegetation.
Physiography .^ — "In streams, current and oxygen content are
determined very largely by physiographic conditions. Current is a
function of volume of water and slope of stream bed. Oxygen content
is largely determined by the rate of flow, and therefore is influenced by
physiography. In lakes, oxygen content is determined by the depth,
the temperature, and winds — physiographic factors are again important.
On land, moisture and light are in a measure controlled by physio-
graphic features. Slope and direction of facing profoundly affect
vegetation, moisture, and light." (Shelford.)
Siirface Materials and Vegetation.^" Materials for abode are
largely the surface soil or rock or the vegetation. Surface soil or rock
influences the moisture. Both moisture and surface materials influ-
ence the kind and amount of vegetation. All are interdependent.
"Physiographic features change with time. Erosion changes the
gradient of streams, the width of valleys, the steepness of valley walls
and cliffs, the ground- water level, etc. The weathering of rock is a
process familiar to all. It is the aggregate of processes by which the
coarse' and hard or massive materials are reduced to clay and soil.
This requires time.
"The fact that vegetation grows upon the so-called sterile, coarse,
rough-surface materials, usually scattered or ephemeral at first, but
increasing in denseness with each generation, is also familiar. Plants
add organic matter to the soil. This organic matter holds the water
so that moisture increases and plants may increase. With such changes
it is obvious that an area of sterile soil will support more animals as
time goes on, than at the outset, when the conditions were such that
only a few hardy species could live. Here again, then, time is the
important factor in determining the change of the area, so as to be
suitable for more species (because more species are adapted to live in
the resulting than in the initial conditions) . The length of time which
has elapsed since a given set of surface and physiographic conditions
became exposed to the atmosphere is very important in governing the
number, kind, and distribution of animals in a given area." (Shelford.)
INSECT ECOLOGY 389
IV. Classification of Environments
The distinction must be made between climatic environmental
complexes and local complexes. "The climate, and such features as
types of vegetation covering large areas, e.g., steppe, deciduous forest,
etc., are commonly regarded as climatic. Opposed to these, and lying
within them, are the local conditions, such as streams, lakes, soils,
exposure, etc., which are only indirectly dependent upon climate."
(Shelford.)
The classification of animal environments is based upon vegetation,
physiography, or both. Where vegetation exists, animal communities
are referred to the plant communities which form their environments.
(Plate V.)
The simple and natural classification of plant communities recom-
mended by Livingston and Shreve is illustrated as follows:
"The extensive areas such as the sagebrush plains of the Great
Basin, the grasslands of Nebraska and Kansas, or the pine forests of
the Atlantic Coastal Plain are designated sls formations . The smaller
and less markedly differentiated areas within a formation are designated
as associations, as, for example, the forests of shortleaf pine in New
Jersey, those of loblolly pine in Maryland and Virginia, and those of
longleaf pine in the Gulf States, all lying within the Coastal Plain
formation. The smallest units of vegetation are [sometimes] termed
societies, and these are of small area and represent portions of the associa-
tion in which a definite aggregation of species is to be found." (Living-
ston and Shreve.)
An outline of the content of animal ecology prepared by a committee
of the Ecological Society of America, in 1920, contains the following
useful synopsis.
Distribution of Communities
I. Land communities.
(a) Forests with broad thin leaves.
1. Continuously moist and evergreen.
(a) Uniformly warm, affording habitats in six or more strata. (Tropical
rain forests.)
(6) With cool season. (Temperate rain forests.)
2. Intermittently dry or cold, and deciduous.
(a) Warm with distinct dry season. (Tropical deciduous forest.)
(b) With cold winter, little winter shelter. (Temperate deciduous forest.)
(b) Communities of evergreen forests of narrow, thick leaves.
1. Moist conifer forest with little undergrowth.
2. Rainy conifer forest with shrub undergrowth.
5. Open, arid, conifer forest.
390 ENTOMOLOGY
(c) Communities of sav^anna and grassland.
1. Tropical savanna (dry season) affording habitats in groves, thickets, forest
margins and grasslands.
2. Tropical steppe; large herds of mammals.
3. Temperate savanna; habitats in groves, thickets, forest margins and
grasslands.
4. Temperate steppe with cold or dry winters and usually large herds of
mammals.
5. Arid, broken, bush-covered steppe with small herds of mammals.
((f) Communities of winter rain (forests with broad thick leaves) e.g., California
semi-desert,
(e) Communities of desert and semi-desert.
1. Grass, cactus, tree semi-desert with grazing mammals (e.g., South Texas
semi-desert); succulent semi-desert; shrub-covered semi-desert.
2. Extreme desert without large diurnal mammals.
(/) Arctic and Alpine lands.
1. Tundra.
2. Alpine meadows. /
3. Ice fields.
2. Communities of waters and shores.
(a) Communities of the sea (Marine).
1. Communities of the open sea (Pelagic).
(a) Mid-oceanic communities.
(b) Oceanic island communities.
(c) Sargassum communities.
(d) Coastal oceanic communities.
2. Communities of the sea bottom (Benthic).
3. Littoral communities.
(a) Communities of eroding shores; subdivisions based on exposure,
bottom material and latitude.
(fi) Communities of depositing shores; subdivisions as above plus vegeta-
tion.
(c) Special communities: coral; tidepools; kelp.
3. Communities of the sea shores. Animals feeding in the sea and breeding on the land,
or vice versa. Classification based on climate.
4. Communities of the fresh waters.
(c) Communities of still waters. Subdivisions based on size, depth and vegetation;
littoral, pelagic, benthic.
(b) Communities of turbulent waters. Sbdivisions based on character of water
movement.
(c) Swamps, marshes, etc.
Ecology finds its distinctive field of study in communities and
succession. These important subjects can not, however, be adequately
presented from an entomological viewpoint alone. Furthermore, little
has been published on the subject as regards insects. The most that
can be done here is to illustrate the subject by naming some of the better
known insects as being characteristic of a few typical environments,
and to add occasional remarks on adaptation in relation to habitat.
Plate V.
€01 Bli
INSECT ECOLOGY 395
V. Communities
In a given habitat the fauna and flora together constitute a biota.
The term fauna is generally used in connection with classification or
geographical distribution, as is also the term flora. In reference to
ecological relations, however, the animals or plants of a given habitat
constitute a community.
As animals and plants, according to their structural resemblances or
differences, fall into species, genera, families, orders, etc., so do animal
or plant communities, according to their ecological likenesses or unlike-
nesses, fall into mores, consocies, strata, associations, and formations;
each of these orders being inclusive of the preceding kind; there the
resemblance ends. The animals of a community agree in their reactions
to the factors that they encounter. If they meet environmental influ-
ences in the same way, they are said to be ecologically similar; if they
meet the same influences in different ways, they are ecologically equiva-
lent. Thus a caterpillar that meets low temperature by making a co-
coon, and one that gets the same result by digging into the ground,
are ecologically equivalent. Animals select their habitats, probably by
trial and error; and their behavior becomes adjusted to the surrounding
conditions. (Shelf ord.) ' ' The habitat is the mold into which the organ-
ism fits. Since habitats are different, animal communities occupying
different habitats are physiologically different. Communities are sys-
tems of correlated working parts." (Shelford.)
''Mores are groups of organisms in full agreement as to physiological
life histories as shown by the details of habitat preference, time of
reproduction, reactions to physical factors of the environments, etc.
The organisms constituting a mores usually belong to a single species
but may include more than one species.
"Consocies are groups of mores usually dominated by one or two of
the mores concerned and in agreement as to the main features of habitat
preference, reaction to physical factors, time of reproduction, etc.
Example: the prairie aphid consocies. The aphids dominate a group of
organisms which for the most part prey upon them, as, for instance,
certain species of lacewing, lady beetles, syrphus-flies, etc.
"Strata are groups of consocies (and animals not so grouped) occupy-
ing the recognizable vertical divisions of a uniform area. Strata are in
agreement as to material for abode and general physical conditions but
in less detail than the consocies which constitute them.
"For example, a forest-animal community is clearly divisible into
394 ENTOMOLOGY
the subterranean-ground stratum, the field stratum (zone of the tops
of the herbaceous vegetation), the shrub stratum (zone of the tops of
the dominant shrubs), the /ou'erZ/'gestratum (zone of the shaded branches
of the trees), and the upper tree stratum. A given animal is classified
primarily with the stratum in which it breeds, as being most impor-
tant to it, and secondarily with the stratum in which it feeds, etc., as in
many cases most important to other animals. The migration of ani-
mals from one stratum to another makes the division lines difficult to
draw in some cases. Still, the recognition of strata is essential but a
rigid classification undesirable. Consocies boring into the wood of
living trees probably should be considered as consocies relatively
independent of stratification phenomena.
^^Associations are groups of strata uniform over a considerable area.
The majority of mores, consocies, and strata are different in different
associations. A minority of strata may be similar. The term is
applied in particular to stages of formation development of this ranking.
The unity of associations is dependent upon the migration of the
same individual and the same mores from one stratum to another at
different times of day or at different periods of their life histories.
Migration is far more frequent from stratum to stratum than from one
association to another.
"Formations are groups of physiologically similar associations.
Formations differ from one another in all strata, no two being closely
similar. The number of species common to two formations is usually
small (e.g., 5 per cent.). Migrations of individuals from one formation
to another are relatively rare." (Shelford.)
VI. Examples of Insect Communities
The article by A. G. Vestal, from which the following extracts are
taken, though limited to a single group of insects, the grasshoppers,
is a good example of how entomological field observations may be
organized on an ecological basis. The observations were made at
Douglas Lake. Michigan.
Community-relations of Grasshoppers
Northeastern Conifer Formation.— r//w/a Association. — Cedar and
peat bog. Melanoplus islandicus the only species.
Aspen Association. — In treeless parts, M. angustipennis is the
common species. M. luridus is found sparingly in scattered aspen
INSECT ECOLOGY 395
growths. Scirtetica marmorata occurs usually on or near the hchen-
covered surfaces.
Eastern Deciduous Forest Formation. — Herbaceous Associations. —
Hot dry clearings. Grasshoppers are numerous both in individuals and
in species. In order of abundance: Melanoplus atlanis, Camnula
pellucida, Dissosteira Carolina (Carolina locust), etc.
Thicket and Bramble Associations. — :M. bivittatus occasional on
shrubs. M. atlanis and others occur on the ground.
Local Associations. — Dry Beach. — Pure sand, dry and shifting,
with full exposure to sun and wind. Here are several species of grass-
hoppers, which occur also in other habitats. Trimerotropis maritima
(the seaside grasshopper, p. 196) is, however, limited to this habitat,
and has the same brownish color as the sand.
Marsh Associations. — Several species of grasshoppers are found in
the tall, rather close, sedge or grass growths. Stenobothris curtipennis
is the characteristic grasshopper of littoral situations.
Ruderal Associations. — Dry Grassland. — Waste places, dry pastures,
abandoned fields, roadsides, etc. In order of importance: M. atlanis,
Camnula pellucida, M. bivittatus, Dissosteira Carolina, Arphia pseudo-
nietana. All these species, with the possible exception of the last, are
more abundant in ruderal than in native vegetation.
Sparsely Vegetated or Bare Soil. — The CEdipodinae normally rest on
bare soil and oviposit in it. Bare soil as a habitat is, however, not
sufficient; nearby vegetation is necessary. Grasshoppers are rare on
extensive areas of bare soil, except at the borders. They are conspicu-
ous on bare places, but are more abundant in the interspaces between
plants, in open growths. The Carolina locust, Dissosteira Carolina, is
the most familiar species of bare soil, though other species have the
same habitat.
Meadow Associations. — Variable in character. In a bluegrass- white
clover meadow, M. atlanis and Stenobothris curtipennis are of about equal
abundance. The red-legged locust, M . femur-rubrum is more abundant
than these in such places, in some localities. The differential locust,
M. dijferentialis , is typical in meadow habitats.
1. Grasshoppers are more abundant, in species and in individuals,
in herbaceous or grassland habitats than in forest, and more abundant
in dry than in moist or wet situations.
2. Certain species are much more restricted than others in range of
habitats, and in accompanying range of toleration of physical and
vegetational factors of the environment.
396 ENTOMOLOGY
3. Although a species may be found over several associations, it is
more abundant in one, or two, of these, than in others. Certain activi-
ties take place in more restricted habitats; chief of these restricted
activities is the laying of eggs.
4. No two plant associations have identical grasshopper assemblages.
5. No two grasshopper species have identical habitat-preferences.
It should be said that these scanty excerpts give no idea of the scope
of Vestal's article; most important in which are the ecological generaliza-
tions.
Mr. A. P. Morse, authority on Orthoptera, has paid particular atten-
tion to the subjects of distribution and adaptation. His data were given
according to life zones and habitats, but are rearranged here as follows.
Shores of Seas and Lakes. — Bare sands, hot and dry. Ground
Stratum. The seaside locust, Trimerotropis maritima, found along the
Atlantic coast from Maine to North Carolina, and inland about the
Great Lakes, is a characteristic arenicolous (sand-dwelling) species,
which varies in color from gray to brown, in harmony with its local
habitat (see p. 196).
Salt Marshes and Vegetation Bordering Brackish Waters. — Moist
Soil. Ground and Herbaceous Strata. Orphulella olivacea, occurring
along the Atlantic coast from Connecticut to Florida and Texas; the
only halophilous (inhabiting salty soil) locust of the Eastern States.
Semi-Arid Areas. — Hot and Dry. Herbaceous and Shrub Strata.
Eesperotettix pratensis, ranging from Mexico and Texas to Washington,
and California to Indiana; occurring also in the Southeastern States a-
mid conditions much resembling those of its habitats in the arid West;
for example along the Gulf shore of Florida, among the xerophytic
(inhabiting hot, dry places) strand vegetation.
Temperate Savanna and Grassland Formation.— Heihsiceons Stratum.
Orphulella picturata and Melanoplus bispinosus are common on the
prairies west of the Mississippi. In damp grassy fields the red-legged
locust, Melanoplus femur-rubrum, is common; in dry grassy fields, M.
atlanis. On ruderal dry grasslands are species of Arphia, Syrbula, etc.
On bare soil, hot and dry, are the Carolina locust, Dissosteira Carolina,
and Trimerotropis citrina. On the moist banks of streams, M. femora-
tus. On moist soil of sandy loam, or the banks or beds of freshwater
streams, somewhat exposed, are the grouse locusts, Tetriginae, some of
which feed sometimes on humus. On bunch-grass in fields or openings
in the forest is Eesperotettix brevipennis, limited to this plant.
Temperate Deciduous Forest Formation. — In the undergrowth is Mela-
INSECT ECOLOGY 397
noplus strumosus. On bare or lichen-crusted rock occurs Trimerotropis
saxatilis (see page 197), which occupied that station before the forest
came.
Adaptations. — "Brachypterism (the short-winged condition) in
locusts is a more complete adaptation to a leaping mode of progression
brought about by life in situations where flight is difficult or impracti-
cable, and consequently disadvantageous. That this is the true ex-
planation is indicated by the habits and haunts of the majority of the
flightless species (sylvan surroundings or tangled undergrowth wherever
found); by their distribution locally, horizontally, and vertically; and
by the equally characteristic habits, haunts, and distribution of macrop-
terous (long- winged) species as inhabitants of the open field, desert, or
savanna.
"The advantages of progression by fiight^dispersal widely and
easily effected, often aided by the wind, ease of escape from many ene-
mies, etc., and the superiority of this mode in open lands — are evident
to all. On the other hand, long wings and locomotion by flight are
disadvantageous amid dense underbrush, where a leaping mode of
progression has decided advantages. Organs unused or disadvanta-
geous tend to dwindle and disappear; hence the loss of wings.
"It is found that Orthoptera frequenting habitats involving passage
over open spaces of considerable extent, such as fields, between trees in
forests, and bushes or thickets in deserts, are usually long-winged, flying
species; and others dwelling in an environment of more or less dense,
intricate, interlacing vegetal growth, be it sub-alpine or sub-tropical,
in forest or swamp — or in burrows, crevices, etc., — in short, in stations
where wings are not needed or are at a disadvantage, are very generally
apterous (wingless) or brachypterous (short-winged).
"Brachypterism, therefore, appears to be largely not so much a case
of natural selection through the agency of the wind as an adaptation in
structure to habits. The fact that the heavier-bodied female is more
frequently or completely brachypterous than the male and that the teg-
mina in the latter sex when used as musical organs are retained in a
less degenerate condition (even when entirely useless in flight) , confirms
this explanation of brachypterism." (A. P. Morse.)
Communities of Streams
From Shelf ord's notable volume. Animal Communities in Temperate
North America, we may take, from the wealth of data given, examples of
common insects representing the various communities of streams.
398 ENTOMOLOGY
Intermittent Stream Communities. Temporary rapids consocies. —
The larva of the black-fly, Siniulium, found in the smallest trickle of
water. Nymphs of May flies, as the stream grows a little larger. No
permanent aquatic residents, however, in these temporary streams.
The temporary residents may fail to transform if the water dries out too
soon. Temporary pool consocies. — -Somewhat more permanent. Insects
that belong primarily to stagnant ponds make their appearance.
Permanent pool communities. — A practically permanent fauna. Water
striders, back-swimmers, water boatmen, etc. are common. Dragon fly
nymphs, diving beetles, crane fly larvae, and many other insects.
Spring Brook Associations. — In streams fed by springs. On the
stones, larvae of the black-fly, Simulium, and the caddis fly, Hydropsyche.
Under the stones, nymphs of May flies and larvae of flies and midges
{Chironomus, Dixa).
Swift-stream Commimities. Hydropsyche or Rapids Formation. —
Three ecologically equivalent modes of life, each meeting the current in
a different way. These are (i) clinging to stones in the current, (2)
avoiding the current by creeping under stones, (3) self-maintenance by
strong swimming powers. Upper surface of stones (stratum i) :
black-fly larvae, hanging from stones to which they are attached by
means of a sucker at the posterior end of the body. Caddis worms,
Hydropsyche, in cases made of pebbles; with a net for catching floating
food. Among the stones (stratum 2) : miscellaneous insects, also of the
following stratum. Under the stones (stratum 3) : May fly nymphs,
larvae of midges, Chironomus, and of horse flies, Tabanus. Stone fly
nymphs, Perlidae, with flattened bodies. Larvae of the parnid beetle
Psephenus. Caddis worms, Helicopsyche. Nymphs of the damsel
fly, Calopteryx, if vegetation is present. Sandy and gravelly bottom forma-
tion (pools). — Bloodworms, Chironomus. The burrowing dragon fly
nymph, Gomphus exilis, a burrowing May fly nymph, caddis worms.
Sandy Bottomed Streams.- — With shifting bottom, the animals
present being those which belong to moderately swift water. Brook
beetles, Parnidae, attached to the few scattered plants. On logs and
roots, many Parnidae; predaceous diving beetles, Dytiscidae, hiding in
the crevices; a few caddis worms, Hydropsyche; the little dytiscid,
Hydroporus mellitus, which buries itself in the sand.
Sluggish Stream Commimities. Sand and Silt Bottom Formations. —
Bloodworms, Chironomidas ; green midge larvae, Chironomidae ; occa-
sional caddis worms, Hydropsyche; a burrowing May fly nymph,
Hexagenia. Formation of the Vegetation. — A densely rooted vegetation.
INSECT ECOLOGY 399
as in ponds. Large numbers of diverse insects, rnany of which come
to the surface for air, both in the adult and the young stages. Water
scorpions, Ranatra; creeping water bugs, Pelocoris femoratus; small water
bug, Zaitha fluminea; water boatmen, Corixa; predaceous diving beetles,
Dytiscidae; water scavenger beetles, Hydrophilida;. The gilled aquatic
insects are the May fly nymphs, Ccenis and Callihcetis; damsel fly
nymphs, Ischnura verticalis; diagon fly nymphs, ^^schnidae and
Libellulidaj; these utilizing the vegetation as resting-places or clinging-
places, or as a means of creeping to the surface to transform.
Tension Lines. — Margins of bodies of water, swamps and marshes,
and temporary ponds are on the border line between land and water.
The classification of the communities of such tension lines of overlapping
environments is often diflicult. (Shelford.)
Along the margins of young ponds and lakes is an area which is
characterized by being made up of wet sand or mud which is submerged
at high water and moist at other times. Here we find springtails
(especially Poc^wm aquatica), shore bugs (Saldidae), many tiger beetles
(Cicindelidae) and numerous small flies. The ground beetle {Bemhidion
cannula) and numerous scavengers (Staphylinidas, Histeridae, etc.)
are common because the beach is often strewn with dead animals which
have floated ashore. (Shelford.)
In Shelf ord's Animal Communities there are extended accounts of
communities of streams, lakes, ponds, prairies, and forests.
Community Relations in New Mexico
The notes that follow on the insect ecology of New Mexico are taken
from an interesting report by Professor J. R. Watson. They are
here arranged under four of Livingston's vegetational areas.
Northern Mesophytic Evergreen Forest Formation. Douglas
Spruce Association. — Poor in insect life. Some thirty species listed. The
carpenter ant, Camponotus pennsylvanicus , is common here and in the
yellow pine association, but was not seen outside of the mountains.
The butterfly, Grapta zephyrus, is also limited to these two associations.
The familiar mourning cloak butterfly, Vanessa antiopa, is present.
Yellow Pine Association.- — About fifty species of insects listed. Machi-
lis sp. The hemipteron Oncometopia lateralis is confined to this asso-
ciation. Circotettix undulatus is very rare outside of this association;
it makes the loudest noise of any grasshopper in the region. Another
locust, Arphia acta, noteworthy for its loud crackling noise, is common,
and descends into the cedar association.
400 ENTOMOLOGY
Western Xerophytic Evergreen Forest Formation.— A dwarf and
open form of semi-forest that characterizes the edges of the preceding
formation. Pinon Association.- — The locust, Trimerotropis cyanea, is
especially at home here. The hemipteron, Perihalus limbolarius, is
very abundant on blossoms of Yucca. The skipper butterfly Epargyreus
tityrus seems to belong here. Cedar Association. — The tarantula killer,
Pepsis formosa, is particularly abundant here. On milkweed, which is
more abundant here than elsewhere, is the cerambycid beetle, Tetraopes
iemoratus, and the hemipteron, LygcBUs turcicus.
Desert-grassland Transition Formation. — Intermediate between
the Grasslands to the east and the Desert regions to the west. Opuntia
arborescens Society.— Several insect species are quite characteristic of
this society. The nitidulid beetle, Carpophilus pallipennis, eats the
pollen and petals of the Opuntia and every blossom commonly shows
from a dozen to a hundred or more individuals. The peculiar ceram-
bycid beetle, Presmis pocularis, and the next insect are chiefly respon-
sible for weakening and kilHng the cactus plants. The beetle apparently
never leaves the plant, and its wings are degenerate. The female is
usually seen carrying her much smaller mate. The larvae bore in the tis-
sues of the plant. The cicada, Cacama valvata, is very abundant on the
tree cactus, but, unlike the last, also occurs on the prickly pears. The
loud calls of the males are heard on every hand when the sun is shining.
But let a cloud obscure the sky for a moment and all is hushed. The
larvae feed on the roots of the cactus. Shortgrass Association. — The mesa
grasshopper, Trimerotropis vinculata is extremely numerous, ascending
even into the yellow pine association. It is very variable in color and
the variations have a very definite relation to that of the ground around
them, being very light on sandy soil, mottled on pebbly hills and darker
among the pines where there is more vegetation. The species migrates
in large numbers when the rains cease and the grasses on which it feeds
dry out. Many species of insects inhabit the mesa. Here lives the
harvesting ant, Pogonomyrmex occidentalis (see page 297). It is well
known that these ants bring their stores of grain out to air occasionally.
Professor Watson relates that "One somewhat windy day in September,
a hill was visited in which part of the ants were busily engaged in
bringing out the grain to air and others were as busily engaged in
carrying it back again. One ant would drop a grain and at once start
back without a load into the hill for another, whereupon the grain
would be at once seized by another ant and carried back into the gran-
ary. It is possible that this treatment is what the grain needed but it
INSECT ECOLOGY 4OI
looked to the interested observer like a serious disagreement in the
colony as to where that grain should be, a case illustrating the limita-
tions of instinct in developing 'team work.' "
Large centipedes, Scolopendra, are quite common, often entering
houses and being much feared; though their bite is by no means as
serious as represented. The whip-scorpion, Thelyphonus, "is rarely
met with on the mesa. Though probably poisonous, its bite is also
grossly exaggerated in popular belief. " (Watson.) Tarantulas, Lycosa,
"are somewhat more common than the last but much less so than the
centipedes. Their bite is more serious than any of the above, but still
not dangerous to most people." (Watson.)
Rio Grande Semi-desert Formation. — Hot and dry. Gutierrezia
Association. — The big clumsy sand-cricket, Stenopelmalus fasciatus,
is common under stones, etc. Several species of the tenebrionid sub-
family Eleodinae are characteristic. One of these beetles, Eleodes
longicollis, when held, can squirt an ill-smelling fluid to a distance of
eight inches. The large black tenebrionid beetles, Eusattus convexus,
"form a very large and characteristic feature of the fauna of this region.
They are true children of the desert. Their elytra are grown together
and to their backs, an adaptation to the fierce sand storms of the mesa.
These wind storms drifting sand and gravel with them are a source of
grave danger to the fauna of the region, even to man himself. The
author has several times been caught out on the mesa when one struck
the region with its usual suddenness and has stopped to observe the
behavior of the animals. The prairie horned larks sought the shelter
of the friendly arroyo banks. (The author has picked up these birds
on the mesa during one of these storms. They were so exhausted by the
buffeting that they had received that they made no effort to escape.)
The digger wasps climbed into the Gutierrezia bushes and hung on for
dear life with all of their feet wrapped about the stem, an attitude that
they also assume during a shower; the snout beetles on the other hand
backed down off the Gutierrezia and sought shelter in the ground; the
woolly bears and other caterpillars curled up under the shelter of tufts
of grass; most of the lizards sought their holes as did the harvester
ants; but these Tenebrionidae went about their business as usual entirely
oblivious, apparently, of the storm. Their heavy bodies kept them
from being blown away and their heavy coat of chitin (it is hardly
possible to force a heavy insect pin through some species) defied the drift-
ing wind. In their disposition not to be too particular as to what they
eat they again show that they are true children of the desert. Anything
402 ENTOMOLOGY
from the tender green seedling leaves of a Hoflfmanseggia to a dead
member of their own species is good. They collect in large numbers
about the carcass of a dead mammal. They will come out from their
winter quarters under the rosettes of Yucca and other sheltered places
any time in winter if it is as warm as 60° F. They have been taken by
the author on January 15. On the other hand they seem somewhat
to shun the hottest hours of the day in summer, being then much more
noticeable toward sunset." (J. R. Watson.)
In the shallow depressions or "draw" in the mesa above the place
where a definite arroyo develops, there is found a society of which
certain quick-growing annual grasses are most conspicuous. "Here
and here only have I ever found this big, nearly wingless, 'lubberly
locust ' (Brachystola magna) , a good illustration of an insect restricted
to a very limited habitat. " (Watson.) The grasshopper, Heliastus
aridus, is particularly abundant in these arroyos, where its mottled
colors agree perfectly with the gravelly surface.
Chrysothamnus Association. — Occupying such rapidly eroding and
hence unstable situations as the dissected edge of the mesa and the
higher gravelly parts of the valley of the Rio Grande, this is the most
xerophytic (inhabiting hot dry places) of the associations. The charac-
teristic tenebrionid beetle, Cysteodemus wislizeni, is very common in
colonies, which are spread over much ground. The ambush bug,
Phymata erosa fasciata is very abundant; it is almost perfectly concealed
in yellow blossoms, as those of golden rod, where it occurs more com-
monly than in white blossoms. The clear-winged moth, Calesesia
coccinea, is exceedingly abundant on Hymenopappus during the third
week in May; its conspicuous colors blending perfectly with those of the
blossoms of this plant. The insect disappears by the first of June.
The magnificent noctuid moth, Erebus odora, is occasionally taken.
The sand dunes are entirely barren of vegetation and of insect life
except for a species of digger-wasp, Bembex, which here finds conditions
favorable for its colonies. "All the specimens of the scorpion {Buthus)
that I have seen have come from this association. Its sting is, to
most people, not nearly as serious as it is represented to be. Persons
that have experienced it say that for a short time only is the pain more
severe than that resulting from the sting of a hornet and that it does
not last as long. " (Watson.) In the Croton Society the short-winged,
tricolored, or "barber-pole" grasshopper, Dactylotum pictum, occurs
wherever its food plant, Croton texensis, occurs in sufficient abundance.
The walking-stick, Diapheromera femorata, is present also. It is, of
INSECT ECOLOGY 403
course, perfectly harmless, but is charged by the natives with causing
the death of many a poor horse.
In the "Valley" insects are abundant in number of species and of
individuals; but the term valley does not signify much, ecologically,
since it may mean anything from mud flats to desert. On the mesa,
dragon flies range five or six miles from any possible breeding place,
but the feebler damsel flies never fly far from home. The harlequin
cabbage bug is sometimes abundant on Cleome and on cabbage sprouts,
but does not seem to be a very serious pest, possibly because it prefers
the Cleome. The squash bug, Anasa tristis, is very abundant on culti-
vated squashes, and . commonly hibernates under yucca stems miles
from any cultivated fields. The well-known Carolina locust, Dis-
sosteira Carolina, which in the East frequents the driest of situations,
in New Mexico clings very closely to the moist valleys, like other eastern
forms (as tiger beetles) that occur also in New Mexico. In both east
and west, however, the species frequents places of about the same degree
of humidity. In the Alkaline Meadow Society, the lesser migratory
locust, Melanoplus atlanis, occurs in the more moist situations, and
damages alfalfa in the valleys. The red-legged locust is common,
inhabiting somewhat drier situations than the last species. Mosquitoes,
Culex pipiens, breed in countless millions in the ponds that form in the
valley whenever the Rio Grande is high, usually in May and June. All
the mosquitoes seen on the mesa come from the valley; sometimes they
are five miles from any possible breeding place. They are carried by a
gentle breeze, but a brisk breeze causes them to seek shelter low down
among the herbage and not to venture forth.
The following species, of wide distribution and not characteristic of
any particular formation, are of interest as occurring in New Mexico,
because they are some of the most familiar insects of more eastern states
under quite different climatal conditions. Coleoptera. — The metallic
leaf-beetle, Chrysochus auratus, occurs on Apocynum as usual, but at an
altitude sometimes of ten to eleven thousand feet. Euphoria inda
occurs from the valley up to the yellow pine association and doubtless
higher. The lady-beetle, Hippodamia convergens, is abundant every-
where from the tops of the highest mountains to the lowest parts of
New Mexico. Lepidoptera. — Colias eury theme, is common in the moun-
tains and in the valley wherever there is damp soil, but is absent from
the mesa. The checkered white, Pieris protodice, is found from the
valley to the spruce association. The painted lady, Pyrameis cardui, is
abundant wherever the thistle grows; and more abundant up in the
404 ENTOMOLOGY
blue spruce association than anywhere else. Hymenoptera. — The social
wasp, Polistes variatus, nests fronii the valley of the Rio Grande up into
the spruce forest at eight thousand feet. The pigeon Tremex, T. columba,
is equally abundant in the cottonwoods of the valley and in the Douglas
spruce of the mountains. Hemiptera. — Gerris remigis, the well known
water strider of eastern states, is found on all suitable ponds and streams
in both valley and mountains. The plant-feeding bug, Lygus pratensis,
is as ubiquitous here as it is elsewhere in the United States.
VII. Succession
"Succession is no doubt one of the most important and widespread
of the phenomena discovered by the ecologists up to the present time.
Simply stated, it means that on a given fixed area organisms succeed one
another, because of changes in conditions. These changes make
impossible the continued existence of the forms present at any given
time; with the death or migration of such forms, others adapted to the
changed conditions occupy the area, whenever such adapted forms are
available. The changes referred to result from physical or biological
causes, or combinations of the two. It is probable that the causes of
the changes are frequently complex combinations of various factors.
"We have among the physical causes changes in climate and changes
in topography. All degradation of land is a cause of succession. Such
geological processes are well understood and treated in textbooks on
geology and physiography.
"The biological causes of succession lie chiefly in the fact that organ-
isms frequently so affect their environment that neither they themselves
nor their offspring can continue to Uve at the point where they are now
living. Every organism adds certain poisonous substances to its
surroundings, and takes away certain substances needed by itself. It
frequently thus so changes conditions that its offspring cannot Hve and
grow to maturity in the same locality as the parents. However, by
these same processes it prepares the way for other organisms which can
live and grow in the conditions thus produced." (Shelf ord.)
"The general growth or evolution of environmental conditions
and the communities which belong to them are included under succes-
sion. The word succession is used in three distinct senses. We speak
of (a) geological succession, (b) seasonal succession, and (c) ecological
succession." (Shelford.)
Geological. — "Geological succession is primarily a succession of
species throughout a period or periods of geological time. It is due
INSECT ECOLOGY 405
mainly to the dying-out of one set of species and the evolution of
others which take their places, or in some cases to migration."
(Shelford.)
Many species of insects owe their present distribution primarily to
the phenomena of the glacial epoch. An excellent example of this is
the White Mountain butterfly (page 325). In Arkansas mountains,
the "elevation is not sufficient to provide true boreal conditions, but
does modify the temperature so that certain species, abundant at the
north, and forced southward during the glacial epoch, have been enabled
to exist in this latitude till the present time. Such are the grasshoppers
Tettix hancocki, Chloealtis conspersa, and Melanoplus fasciatus."
(Morse.)
"The chief biological importance of the Southeastern United States,
comprising Virginia, North and South Carolina, Georgia, Florida,
Alabama, eastern Tennessee, and West Virginia, is connected with two
facts: First, this region served during the Glacial Epoch as a refuge for
boreal forms of life which had been pushed southward by the climatal
conditions of the Ice Age, and at the close of that period it became the
center of dispersal whence these forms were able to restock the opening
country at the north. Second, during this later period its lowland
plains served, and probably continue to serve, as a highway of dispersal
for austral forms entering the country from the south and southwest,
many of which have penetrated far into the heavily glaciated region of
the Northern States." (Morse.)
Seasonal. — "Seasonal succession is the succession of species or
stages in the life histories of species over a given locality, due to heredi-
tary and environic differences in the life histories (time of appearance)
of species living there. " (Shelford.) "Successful species are those that
fit wJc the seasonal rhythm with respect to physical conditions,
food, and numerous o'-^r reiatiorxS. " (Shelford.)
Many examples of seasonal succession among insects will occur
to the student of insect life. The seasonal succession of insects is
frequently correlated with that of plants. The cycle of an insect may
be adjusted to that of a plant upon which it depends.
Thus "the Membracidae or tree hoppers are celebrated for the
wonderful variety and complexity of their adaptations to their food
plants. . . . The tree hoppers of the genus Telamona, for example,
feed very largely on the sap of the trees and mainly on the tender
growing twigs. They find optimum conditions for such feeding only
during the comparatively short period in which the tree is making its
4o6 ENTOMOLOGY
growth. They also must find a location and deposit their eggs while
the wood is still soft and tender; otherwise they will be unable to
penetrate to a sufficient depth to protect the eggs from predaceous and
parasitic insects. The result is that we find that they, with a possible
exception, pass the winter in the egg .stage and have a single annual
generation. ... A striking adaptation to a special period in a plant's
growth is shown in the life cycle of Micrutalis calva, the little shining
black seed-like tree hopper. The nymphs are found between the
branches of the blossom head of the Ironweed, Vernonia. This purple
flower appears only in the fall, so that the single generation of nymphs
comes on over 70 days later than its relative that lives in the tree.
"In the case of Ceresa bubalis (the Buffalo tree hopper) and its
vegetation-feeding allies the need of haste is not so great as their food
plants, Composites, Legumes and others, grow all summer, so we find
the nymphal period both longer and later and the adults extending into
the fall." (E.D.Bali.)
The time of appearance of the locust borer, Cyllene robinice, in the
fall coincides with that of the flowers of golden rod, on which the beetles
feed; the coloration of the beetles being protective, as Prof. H. Garman
has observed in Kentucky.
Ecological.— " Ecological succession of animals is succession of
mores over a given locality as conditions change. If species have rela-
tively fixed mores we have succession of species. When mores are
flexible we may have the same species remaining throughout, with
changes in mores. " (Shelford.)
A few examples, from Shelf ord's Vegetation and the Control of Land
Animal Communities, will serve to illustrate this kind of succession.
The stages of forest development are marked by the dominance of
certain species of trees which succeed one another in a rather definite
order. On the sand areas at the head of Lake Michigan, the sequence
is as follows (Cowles). i. Cottonwood Stage. Near the lake shore,
with the sand more or less shifting and rarely with more than a trace of
humus. 2. Pine Stage. With stable sand, considerably blackened by
humus, except in blowouts. 2>- ^^<^(^k Oak Stage. With the sand much
darkened by humus and locally covered with a dry moss or with dead
leaves; grasses and a shrubby undergrowth occur. 4. Red Oak Stage.
Ground with a carpet of leaves and humus; with a well marked shrubby
and herbaceous growth. Red oak, black oak, and white oak; often
hickory also. 5. Beech Stage. The mineral soil is covered with a
thick layer of leaves and humus. Fewer species of trees than in the
INSECT ECOLOGY
407
preceding stage, but a greater number of species of small shrubs, with
a smaller number of individual shrubs. The trees close the overhead
spaces and make a dense shade, while the lower forest is open. Beech
and sugar maple are characteristic. These five stages are linked
together by transitional stages.
Of the many species tabulated by Shelford, the tiger beetles and
grasshoppers may be selected to illustrate succession in relation to forest
development. The tiger beetles, Cicindela, breed in the subterranean
stratum and feed in the ground stratum.
Tiger Beetles of Forest Succession (Shelford)
In these tables C signifies common; F, few; P, present
Stage I
Cottonwood
Pine
Black Oak
Red Oak-
Hickory
5
Beech
C. hpida
C formosa generosa. .
C. sculellaris lecontei.
C. sex guttata
With the tiger beetles the character of the soil, as regards suitability
for oviposition, is the chief factor that determines the presence or
absence of this or that species. C. sexguttata, which comes in with the
white oak- red oak- hickory forest, lays its eggs under loose leaves or in
little irregularities in the ground, which contain a little humus and are
slightly shaded; it is rare, however, in very shady situations, such as
those of the beech and maple forest.
Of the orthoptera named in the following table, numbers i to 6
breed in the subterranean stratum and feed in the ground stratum;
6 feeds also in the vegetation strata; 7 breeds in the ground stratum,
feeds in the herbaceous; 8 and 9 breed and feed in the herbaceous;
10 and II breed and feed in the tree stratum; 12 breeds and feeds in
the subterranean-ground stratum; and 13 in the ground stratum.
The table indicates that the successive changes in vegetation are
accompanied by corresponding changes in the character of the orthop-
teran fauna. Other insects or other animals also illustrate the same
phenomenon of ecological succession. During the successive vegeta-
tional stages the numbers of a species increase until optimum conditions
of habitat are attained, and thereafter decrease.
4o8
ENTOMOLOGY
Orthoptera or Forest Succession (Shelford)
Stage I
Cottonwood
1-2
2
Pine
2-3
3
Black Oak
4
Red Oak-
Hickory
P
c
C
C
P
P
c
c
C
c
c
c
c
c
C
C
F
C
C
F
C
5
Beech
1. Seaside locust, Trimerotropis
marilima
2. Long-homed grasshopper, Psi-
nidia fenesiralis
3. Sand locust, Agenotettix are-
nosus
4. Mottled sand locust, Spharage-
mon ivyotningarum
5. Migratory locust, Melanoplus
atlanis
6. Locust, Melanoplus angusli-
pennis
7- Sprinkled locust, Chloeallis con-
sPersa
8. Texas grasshopper, Scudderia
texensis
9. Tree cricket, Oecanthus fasciatus
10. Tree cricket, Oecanthus angusti-
pennis
ri. Katydid, Cyrtophyllus perspicil-
latus
f2. Camel cricket, Ceuihophilus. . . .
[3. Locust, Melanoplus islandicus.. .
Some species of insects do not appear until the Black Oak stage, and
others not until the Red Oak-Hickory or the Beech-Maple stage.
The causes of animal succession and the control of animal com-
munities are discussed by Shelford, who draws these conclusions, among
others.
"The development of forest on sand or other mineral soil is accom-
panied by an almost complete change of animal species and probably
by a complete change of animal mores.
"Forest development is accompanied by marked changes in soil
and physical factors; animal distribution is more closely correlated
with differences in physical factors than with species of plants.
"Succession of all the animals of the forest communities under
consideration is comparable in principle to that in ppnds. Succession
is due to an increment of changes in conditions produced by the plants
and animals living at a given point. Animals through their effect
upon the soil play an important though minor part in the process.
"The various animal species are arranged in these communities in
an orderly fashion and the dominating animal mores are correlated
with the dominating conditions.
"Taxonomic (structural) species usually have distinct mores.
INSECT ECOLOGY 409
though the same species often has different mores under different
conditions, and different species may have the same mores. Species
and mores are therefore not synonymous.
"Ecology considers together mores that are alike or similar in
their larger characters."
CHAPTER XIV
INSECTS IN RELATION TO MAN
A great many insects, eminently successful from their own stand-
point, so to speak, nevertheless interfere seriously with the interests of
man. On the other hand, many insects are directly or indirectly so
useful to man that their services form no small compensation for the
damage done by other species.
Injurious Insects.- — Insects destroy cultivated plants, infest do-
mestic animals, injure food, manufactured articles, etc., and molest or
harm man himself.
The cultivation of a plant in great quantity offers an unusual oppor-
tunity for the increase of its insect inhabitants. The number of species
affecting one kind of plant — to say nothing of the number of individuals
— is often great. Thus about 200 species attack Indian corn, 50 of
them doing notable injury; 200 affect clover, directly or indirectly; and
400 the apple; while the oaks harbor probably 1,000 species.
The average annual loss through the cotton worm, i860 to 1874, was
$15,000,000, according to Packard; the loss from the Rocky Mountain
locust, in 1874, in Iowa, Missouri, Kansas and Nebraska, $40,000,000
(Thomas) ; and the total loss from this pest, 1874 to 1877; $200,000,000.
The loss through the chinch bug, in 1864, was $73,000,0000 in Illinois
alone, as estimated by Riley. The ravages of the Hessian fly, fluted
scale, San Jose scale, gipsy moth and cotton boll weevil need only be
mentioned.
At times, an insect has been the source of a national calamity, as was
the case for forty years in France, when Phylloxera threatened to ex-
terminate the vine. In Africa the migratory locust is an unmitigated
evil.
Probably at least ten per cent, of every crop is lost through the at-
tacks of insects, though the loss is often so constant as to escape obser-
vation. Regarded as a direct tax of ten cents upon the dollar, however,
this loss becomes impressive. Webster says: "It costs the American
farmer more to feed his insect foes than it does to educate his children."
The average annual damage done by insects to crops in the United
States was conservatively estimated by Walsh and Riley to be $300,000,-
410
INSECTS IN RELATION TO MAN 4II
000 — or about $50 for each farm. "A recent estimate by experts put the
yearly loss from forest insect depredations at not less than $100,000,000.
The common schools of the country cost in 1902 the sum of $235,000,000,
and all higher institutions of learning cost less than $50,000,000, making
the total cost of education in the United States considerably less than
the farmers lost from insect ravages. Thus it would be within the
statistical truth to make a still more starthng statement than Webster's,
and say that it costs American farmers more to feed their insect foes
than it does to maintain the whole system of education for everybody's
children.
"Furthermore, the yearly losses from insect ravages aggregate
nearly twice as much as it costs to maintain our army and navy; more
than twice the loss by fire ; twice the capital invested in manufacturing
agricultural implements ; and nearly three times the estimated value of the
products of all the fruit orchards, vineyards, and small fruit farms in the
country." (Slingerland.)
Though most of the parasites of domestic animals are merely annoy-
ing, some inflict serious or even fatal injury, as has been said. The
gad flies persecute horses and cattle; the maggots of a bot fly grow in
the frontal sinuses of sheep, causing vertigo and often death; another
bot fly develops in the stomach of the horse, enfeebling the animal.
The worst of the bot flies, however, is Hypoderma lineata, the ox-warble,
which not only impairs the beef but damages the hide by its perforations ;
the loss from this insect for one period of six months (Chicago, 1889) was
conservatively estimated as $3,336,565, of which $667,513 represented
the injury to hides.
All sorts of foodstuffs are attacked by insects, particularly cereals;
clothing, especially of wool, fur or feathers; also furniture and hundreds
of other useful articles.
As carriers of disease germs, insects are of vital importance toman,
as we have shown.
Beneficial Insects.— The vast benefits derived from insects are too
often overlooked, for the reason that they are often so unobvious as
.compared with the injuries done by other species. Insects are useful
as checks upon noxious insects and plants, as pollenizers of flowers, as
scavengers, as sources of human clothing, food, etc., and as food for
birds and fishes.
Almost every insect is subject to the attacks of other insects, pre-
daceous or parasitic — to say nothing of its many other enemies — and
but for this a single species of insect might soon overrun the earth.
412 ENTOMOLOGY
There are only too many illustrations of the tremendous spread of an
insect in the absence of its accustomed natural enemies. One of these
examples is that of the gipsy moth, artificially introduced into Massa-
chusetts from Europe; another is the fluted scale, transported from
Australia to Cahfornia. Some conception of the vast restricting influ-
ence of one species upon another may be gained from the fact that the
fluted scale was practically exterminated in California as the result of
the importation from Australia of one of its natural enemies, a lady-bird
beetle known as Novius cardinalis. The plant lice, though of un-
paralleled fecundity, are ordinarily held in check by a host of enemies
(P- 379)-
An astonishingly large number of parasites may develop in the body
of a single individual; thus over 3,000 specimens of a hymenopterous
parasite {Copidosoma truncatellum) were reared by Giard from a single
Plusia caterpillar.
Parasites themselves are frequently parasitized, this phenomenon of
hyperparasitism being of considerable economic importance. A bene-
ficial primary parasite may be overpowered by a secondary parasite,
evidently to the indirect disadvantage of man, while the influence of a
tertiary parasite would be beneficial again. Now parasites of the third
order occur and probably of the fourth order, as appears from Howard's
studies, which we have already summarized. Moreover, parasites of all
degrees are attacked by predaceous insects, birds, bacteria, fungi, etc.
The control of one insect by another becomes, then, a subject of extreme
intricacy.
Insects render an important, though commonly unnoticed, service
to man in checking the growth of weeds. Indeed, insects exercise a vast
influence upon vegetation in general. A conspicuous alteration in the
vegetation has followed the invasions of the Rocky Mountain locust,
as Riley has said; many plants before unnoticed have grown in profu-
sion and many common kinds have attained an unusual luxuriance.
As agents in the cross pollination of flowers, insects are eminently
important. Darwin and his followers have proved beyond question
that as a rule cross pollination is indispensable to the continued vitaHty
of flowering plants; that repeated close pollination impairs their vigor
to the point of extermination. Without the visits of bees and other
insects our fruit trees would yield Httle or nothing, and the fruit grower
owes these helpers a debt which is too often overlooked.
As scavengers, insects are of inestimable benefit, consuming as they
do in incalculable quantity all kinds of dead and decaying animal and
INSECTS TN RELATION TO MAN 413
vegetable matter. This function of insects is most noticeable in the
tropics, where the ants, in particular, eradicate tons of decomposing
matter that man lazily neglects.
Of insects that are directly useful to man, the silkworms and the
several species of honey bees are the most important. Silk is most
valuable as a textile material, but has minor uses. Some of the best
fishing lines are made of silk; and the best "leaders"- — long, tapering,
strong, and practically invisible in the water — are the silk glands them-
selves, after being stretched and dried. These leaders are imported
from the Mediterranean region, but may easily be made from the glands
of our large native silkworms, such as the Cecropia.
Though honey as a food is not as indispensable to us as it was to the
ancients, immense quantities of it are produced annually, and the
demand for it is usually greater than the supply. Beeswax has more
uses than one might suppose. One of its chief uses is for the manufac-
ture of comb ''foundation" for bee hives. Beeswax, though rivaled by
paraffin and ceresin, is better than these for some purposes. It is used
in poHshes for furniture, floors, carriages, automobiles, shoes and other
leather articles, and steel tools; as a coating for shoemaker's thread and
for steel nails; as an ingredient of some varnishes; for the insulation of
electric wires, etc.; for church candles; salves and cosmetics; in sealing
wax and grafting wax; by sculptors for making models; by dentists for
taking impressions; and was anciently used on writing tablets.
Lac, commonly used as sheUac and for lacquer and other resistant
varnishes, is yielded by several species of scale insects, but chiefly
Tachardia lacca, which is abundant in many parts of India on a variety
of plants (Zizyphus, Acacia, Butea, etc.). The lac is a resinous secre-
tion, produced abundantly by the female, and forming with the exuviae a
protective covering over her body.
A coccid that produces considerable quantities of lac occurs in
Arizona on Larrea mexicana.
Several coccids of the genus Ceroplastes, in India and China, produce
white wax, which is highly valued for some purposes but has been
replaced by paraffin for other uses.
The brilliant crimson pigment of the lac-insect of India is extracted
and known to artists as "lake."
The cochineal insect, Dactylopius coccus, is indigenous to Mexico,
but has been transported with its food plant, the prickly pear, to Spain,
India, and elsewhere. From the dried bodies of the females, carmine is
extracted. The cochineal industry, which dates back to the time of the
414 ENTOMOLOGY
Aztecs, attained an immense development until some fifty years ago,
when it began to decline with the discovery of aniline dyes. Even at
present, however, there is a constant demand for cochineal, which is used
for coloring confectionery, fabrics, inks, and druggists' preparations.
The cottony cochineal insect, Dactylopius confusus, ranges through-
out the cactus region of the United States, and contains the same crim-
son fluid as its ally.
The Greeks and Romans obtained a red dye from species of Kertnes
living on an oak. Galls of Cynipidae were once important as a source
of ink.
As articles of human food, some insects are highly nutritious, but
are appreciated chiefly by savages. Not exclusively, however, for the
"manna" of bibHcal times was almost certainly the honey-dew from a
coccid. It is still used by Arabs as food under the name of "man."
The flavor of the large black carpenter ants, Camponotus, which can be
scooped up with the hands in large numbers, appeals to some who would
resent being called savages. White grubs, available in any desirable
quantity, are said to make an excellent salad, high in protein content.
Used in connection with corn they furnish almost a balanced ration for
hogs.
The red Indians formerly used many kinds of insects as food.
Especially dehcious was a bushel of grasshoppers roasted in a hole in
the ground. After all, the grasshopper is more attractive in appearance
and more refined in its choice of food than the much-esteemed lobster.
The Pah Utes of Utah eke out an existence on dried caterpillars, and
annually flock from far and near to harvest the salt-fly of the salt lakes.
The puparia of these flies {Ephydra hians) are washed up on the shore in
such enormous numbers that they can be collected by hundreds of
bushels. After the dirt is removed and the puparium shelled off, the
pupa, which is rather large, supplies a food which is said to be not un-
pleasant to the taste (Aldrich).
According to Dr. Aldrich, the Indians in the vicinity of Mono Lake,
California, collect for food the caterpiUars of the saturniid moth,
Coloradia pandora, from a species of pine tree. The great event of
gathering the crop comes, unfortunately, only every other year; as the
insect has a two-year cycle and only one brood. The Indians dig a
trench around a tree, making the outer wall of the trench vertical; then
beat the caterpiUars off the branches and collect them in the trench.
The dried caterpillars are a great delicacy to the Indians. Aldrich
says they taste like linseed oil.
INSECTS IN RELATION TO MAN 415
Water-boatmen {Corixa) and their eggs are used as food in Mexico,
and are said to have a fine flavor. In Australia the Bugong moth
occurs in millions in certain localities, and the moth itself was formerly
an important article of food with the aborigines (Sharp). The bush-
men of Australia find that the clay of termite mounds makes a solid
meal; and hill tribes of India eat the termites, which have a flavor like
that of almonds. In Africa the migratory locust has been eaten since
history began.
The wise fisherman knows that certain kinds of insects are excellent
bait for fishes, especially at certain seasons. The better known of these
insects are grub worms, grasshoppers and hellgrammites.
A few insects have medicinal properties. Coccids of the genus
Kermes that live on an oak in the Mediterranean region yield a medic-
inal syrup. Another coccid, Llaveia axinus, of Mexico, produces a
peculiar substance known as axin. This is used as an external medic-
inal application, and is of considerable value as a varnish. (Sharp.)
Our native blister beetles and oil beetles possess a blistering or vesicant
property, which is due to the presence of cantharidin in their blood.
The crushed bodies of a Mediterranean species are still used medically
under the name of Spanish fly. In China medicinal properties are
ascribed to many different kinds of insects.
The use of insects as ornaments must not be forgotten. Beetles
with metallic colors or with iridescence, like the diamond beetle of
Brazil, are made up into jewelry. A coccid, Margarodes formicarium,
of the West Indies, found in the soil, where it lives on roots of plants and
is often plowed up, resembles a pearl, and is strung into necklaces, etc.
(Comstock.) The cucujo beetles (Pyrophorus) of tropical America
are the most brilhantly luminous of insects. They are used for orna-
mental display and are said to be serviceable as candles. Their diffused
light is pleasing in its quality, and it is reported that "the smallest
print may be read by moving one of these insects along the lines."
The showy butterflies, moths, and beetles, mounted for purposes of
display, are familiar to all.
In Japan a "fire-box" to hold a charcoal fire is made from a section
of a log, placed on end. For this purpose a log is frequently selected
on account of its natural ornamentation made by the engraver beetles;
or a screen may be made of wood that is carved with tunnels made by
termites.
The unimportant use of insects as playthings need only be alluded
to. In the south, children amuse themselves by attaching the green June
41 6 ENTOMOLOGY
bugs to threads and letting them fly about. In China crickets are
matched against each other in fighting contests.
Many other examples of insects beneficial, more or less, to man
could be given if space permitted.
Doubtless many of us have now and then kept crickets or katydids in
cages because we liked to hear them sing; or have put fire flies in bottles
to watch them glow.
The Japanese, with a national appreciation of nature which is
foreign to this country, are accustomed to do these things. Crickets
and katydids are sold on the streets, at prices equivalent to two to
fifteen cents each, much as flowers are sold here.
As they have a cherry blossom season, they have also a fire fly
season, when it is the common custom to make visits to the country to
procure fire flies. Special trains are even run for these excursions.
Annually the people of Gifu collect many thousands of fire flies,
which are sent to Tokyo and on a certain night are liberated for the
enjoyment of the emperor.
As objects of scientific investigation insects are important, as no
entomologist will deny. They are even economically important in this
respect, for some of the principles of heredity, applicable to the breeding
of domesticated animals, have been worked out with the aid of insects,
particularly the pomace flies, Drosophila.
Introduction and Spread of Injurious Insects. — Many of our worst
insect pests were brought accidentally from Europe, notably the
Hessian fly, wheat midge, codling moth (probably), gipsy moth,
brown-tail moth, European corn borer, elm leaf beetle, leopard moth,
woolly apple aphid, cabbage butterfly, cabbage aphis, clover leaf
beetle, clover root borer, asparagus beetle, imported currant worm and
many cutworms; though few American species have obtained a foothold
in Europe, one of the few being the dreaded Phylloxera, which appeared
in France in 1863.
The gipsy moth (Porthetria dispar) , a native of Europe, where it is
at times a serious pest, was Uberated in eastern Massachusetts in 1868,
and has spread over the eastern half of the state and into New Hamp-
shire, Maine and Connecticut, in spite of all efforts to control it. Small
infestations occur also in New York and Pennsylvania, and in July,
1920, a colony was found in New Jersey, where at present (1922) 410
square miles are infested. The cost of controlling this omnivorous pest
is enormous (see beyond). "The amount expended by the Bureau in
the campaign against the Gipsy Moth, including the appropriation for
INSECTS IN RELATION TO MAN
417
the current fiscal year, is $4,650,000. " (Dr. L. O. Howard, March 28,
1922.)
The brown-tail moth {Euprociis chrysorrkcea) is a native of the Old
World " where it is found from Algiers on the South to Sweden on the North
and from England on the West to the Himalaya Moutains on the
East. Over most of this area it is recognized as a pest of orchards and
forests. " (Dr. W. E. Britton.) This moth was accidentally introduced
into eastern Massachusetts on nursery stock, and first attracted the
attention of entomologists in 1897, since when it has spread over most
of Massachusetts and New Hampshire, into Vermont, Maine, Nova
Scotia and New Brunswick, over all of Rhode Island, half of Connecti-
cut, and into New York. The brown-tail moth has accompanied the
gipsy moth in its work of destruction.
The brown-tail moth spreads locally by means of flight, mostly;
but may be carried great distances commercially, on shipments of young
trees bearing young caterpillars in their winter nests. The first nests
found in Connecticut came on fruit tree seedlings imported in 1909
from a French nursery. (Britton.) The pest has several times reached
nurseries in Illinois on young trees from Belgium and France, but has
each time been eradicated by the state inspection service before it
could spread from the nurseries. In 192 1 the federal inspectors inter-
cepted nests of the brown-tail moth on forty-two shipments from
France, and egg masses of the gipsy moth on one shipment.
These two pests have been fought most vigorously but are not yet
under complete control. It is worth while to give here an account of
the expenditures made up to date (April 5, 1922) in the fight against
the gipsy moth and the brown-tail moth. Mr. A. F. Burgess, who is in
charge of the work, has kindly furnished these figures.
Expenditures by Infested States
(Federal Funds Not Included)
States
Expenditures
From
beginning
of work to —
Expenditures
by towns, in-
dividuals, etc.
Totals
Connecticut
Maine
Massachusetts
New Hampshire
Rhode Island
183,715-55 Dec. I, 1921
435,000.00 do
5,137,000.00 do
186,500.00 Sept. 30, 1921
179,600.00 Dec. 31, 1921
24,409.72 do
161,883.73 do
175,000.00 do
229.50
180,000.00
9,126,927.97
No record
20 , 000 . 00
No record
25,000.00
No record
No record
183,945.05
615,000.00
14,263,927.97
186,500.00
199,600.00
Vermont
New Jersey
24,409.72
186,883.73
New York
175,000.00
Pennsylvania
600 . 00
do
600.00
$6 , 483 , 709 . 00
$9,352, 157.47 $15,835,866.47
4l8 ENTOMOLOGY
Add to this the amount supplied by the Federal Government, and
the total is more than twenty million dollars.
The San Jose scale insect {Aspidiotus perniciosus) , a native of North
China, was introduced into the San Jose valley, California, about 1870,
probably upon the flowering Chinese peach, became seriously destruc-
tive there in 1873, was carried across the continent to New Jersey in
1886 or 1887 on plum stock, and thence distributed directly to several
other states upon nursery stock. At present the San Jose scale is a
permanent menace to horticulture throughout the United States, and is
being checked or subdued only by the vigorous and continuous work of
ojQ&cial entomologists, acting under special legislation. This pernicious
insect occurs also in Japan, Hawaii, Australia and Chile.
The Mexican cotton boll weevil {Anthonomus grandis), which is
found throughout Mexico and in Guatemala, Costa Rica and western
Cuba, crossed the Rio Grande river and appeared in Brownsville,
Texas, about 1892. It either flew across the river or was carried across
in seed cotton. Since then it has extended its range every year until in
1921 it had practically "reached the limit of cotton cultivation."
The beetle hibernates and lays its eggs in the squares or bolls of
cotton; these are injured both by the larva feeding within and by the
beetles, whose feeding-punctures destroy the bolls and cause them to
drop. The annual loss from the weevil is far in excess of $200,000,000.
The pest has now been thoroughly studied by the Bureau of Entomology,
and the adoption of the control methods recommended by the Bureau
enables cotton to be grown at a fair profit; though the days of "bumper
crops" have gone.
The European corn borer {Pyrausta nubilalis), long known in Europe
as a pest of corn, hemp, hops and millet, was discovered near Boston,
Massachusetts, in 191 6, having been introduced probably in hemp sent to
a cordage factory, or in broom corn. In 1919 the borer was found to
be infesting four hundred square miles in the vicinity of Schenectady,
New York, having arrived possibly in bales of broom corn from Austria.
In 1920 the insect had established itself in an area of nineteen hundred
square miles in eastern Massachusetts, southern New Hampshire, and
New York, and appeared in Ontario, Canada. The borer feeds not only
on cultivated plants but also on a great variety of weeds. Energetic
efforts are being made to prevent this destructive insect from spreading
westward into the corn belt.
The green Japanese beetle {Popillia japonica), which in its native
home is not an important pest, was discovered in New Jersey in August ,
INSECTS IN RELATION TO MAN 419
1 91 6, and in Pennsylvania in 1920. It came from Japan probably as
grubs in soil about the roots of iris or azalea plants, but brought none of
its native enemies with it, and spread rapidly in its new environment.
In 192 1 it occupied two hundred and thirteen square miles in New
Jersey and fifty-seven in Pennsylvania.
The injury is done mostly by the beetles, which skeletonize the leaves
of trees and shrubs, both wild and cultivated, destroy ripening fruits,
and have a longer list of food plants than the brown-tail moth.
Extensive operations against the beetle are being conducted by the
Bureau of Entomology in co-operation with the Departments of Agri-
culture of New Jersey and Pennsylvania.
The elm leaf beetle {Galerucella luteola), notorious in southern
Europe as a defoliator of elm trees, entered Maryland about 1837,
spread along the coast as far as southern New Hampshire, and has made
its way into New York, Ohio and Kentucky, killing off thousands of
fine old elms on its way. The only eft"ective means of controlling this
beetle seems to be an arsenical spray.
The leopard moth {Zeuzera pyrina) , another European species acci-
dentally introduced into New Jersey some time before 1879, spread north
into Massachusetts, assisting the elm leaf beetle in its injurious activity.
The leopard moth is not confined to elms, however, though it injures
chiefly elms and silver maples, but attacks more than eighty kinds of
trees and shrubs, and affects fruit trees as well as shade trees. The cater-
pillar does not feed on the leaves but bores into the branches, which
become weakened as a result and are broken off by the wind.
The pink bollworm {Pectinophora gossypiella) , a cotton pest which is
probably a native of southern Asia and occurs also in Africa, Hawaii
and Brazil, entered Mexico and was recently introduced into Texas.
This serious pest is now being eradicated by the Department of Agri-
culture, at an annual expense of about half a million dollars.
An insect often passes readily from a wild plant to a nearly related
cultivated species. Thus the Colorado potato beetle passed from the
wild species Solarium rostratum to the introduced species, Solanum
tuberosum, the potato. Many of our fruit-tree insects feed upon wild, as
well as cultivated, species of Rosaceae; the peach borer, a native of this
country, probably fed originally upon wild plum or wild cherry. Many
of the common scarabaeid larvae known as 'white grubs " are native to
prairie sod, and attack the roots of various cultivated grasses, including
corn, and those of strawberry, potato and other plants. The chinch
bug fed originally upon native grasses, but is equally at home on cul-
420 ENTOMOLOGY
tivated species, particularly millet, Hungarian grass, rice, wheat,
barley, rye and corn. In fact, the worst corn insects, such as the chinch
bug, wireworms, white grubs and cutworms, are species derived from
wild grasses.
Even in the absence of cultivated plants their insect pests continue
to sustain themselves upon wild plants, as a rule; the larva of the
codling moth, for example, is very common in wild apples and wild
haws.
The Economic Entomologist. — To mitigate the tremendous dam-
age done by insects, the individual cultivator is almost helpless without
expert advice, and the immense agricultural interests of this country
have necessitated the development of the economic entomologist, the
value of whose services is universally appreciated by the intelligent.
Almost every State now has one or more economic entomologists,
responsible to the State or else to a State Experiment Station, while the
general Government attends to general entomological needs in the most
comprehensive and thorough manner.
"It is the special object of the economic entomologist," says Dr.
Forbes, "to investigate the conditions under which these enormous
losses of the food and labor of the country occur, and to determine, first,
whether any of them are in any degree preventable; second, if so, how
they are to be prevented with the least possible cost of labor and money;
and, third, to estimate as exactly as possible the expenses of such pre-
vention, or to furnish the data for such an estimate, in order that each
may determine for himself what is for his interest in every case arising.
"The subject matter of this science is not insects alone, nor plants
alone, nor farming alone. One may be a most excellent entomologist
or botanist, or he may have the whole theory and practice of agriculture
at his tongue's end, and at his fingers' ends as well, and yet be without
knowledge or resources when brought face to face with a new practical
problem in economic entomology. The subject is essentially that of
the relations of these things to each other; of insect to plant and of plant
to insect, and of both these to the purposes and operations of the farm,
and it involves some knowledge of all of them.
"As far as the entomological part of the subject is concerned, the
chief requisites are a familiar acquaintance with the common injurious
insects, and especially a thorough knowledge of their life histories, to-
gether with practical familiarity with methods of entomological study
and research. The life histories of insects lie at the foundation of the
whole subject of economic entomology; and constitute, in fact, the
INSECTS IN RELATION TO MAN 42 1
principal part of the science; for until these are clearly and completely
made out for any given injurious species, we cannot possibly tell when,
where or how to strike it at its weakest point.
"But besides this, we must also know the conditions favorable and
unfavorable to it; the enemies which prey upon it, whether bird or insect
or plant parasite; the diseases to which it is subject, and the effects
of the various changes of weather and season. We should make, in fact,
a thorough study of it in relation to the whole system of things by which
it is affected. Without this we shall often be exposed to needless alarm
and expense, perhaps, in fighting by artificial remedies, an insect already
in process of rapid extinction by natural causes; perhaps giving up in
despair just at the time when the natural checks upon its career are about
to lend their powerful aid to its suppression. We may even, for lack
of this knowledge, destroy our best friends under the supposition that
they are the authors of the mischief which they are really exerting
themselves to prevent. In addition to this knowledge of the relations
of our farm pests to what we may call the natural conditions of their life,
we must know how our own artificial farming operations affect them,
which of our methods of culture stimulate their increase, and which, if
any, may help to keep it down. And we must also learn where strictly
artificial measures can be used to advantage to destroy them.
"For the life histories of insects, close, accurate and continuous
observation is of course necessary; and each species studied must be fol-
lowed not only through its periods of destructive abundance, when it
attracts general attention, but through its times of scarcity as well, and
season after season, and year after year.
"The observations thus made must of course be collected, collated
and most cautiously generahzed, with constant reference to the con-
ditions under which they were made. No part of the work requires
more care than this.
"This work becomes still more difficult and intricate when we pass
from the simple life histories of insects to a study of the natural checks
upon their increase. Here hundreds and even thousands of dissections
of insectivorous birds and predaceous insects are necessary, and a care-
ful microscopic study of their food, followed by summaries and tables
of the principal results, a tedious and laborious undertaking, a specialty
in itself, requiring its special methods and its special knowledge of the
structures of insects and plants, since these must be recognized in frag-
ments, while the ordinary student sees them only entire.
"If we would understand the relations of season and weather to the
42 2 ENTOMOLOGY
abundance of injurious insects, we are led up to the science of meteor-
ology; and if we undertake to master the obscure subject of their diseases,
especially those of epidemic or contagious character, we shall find use
for the highest skill of the microscopist, and the best instruments of
microscopic research.
"All these investigations are preliminary to the practical part of our
subject. What shall the farmer do to protect his crops? To answer
this question, besides the studies just mentioned, much careful experi-
ment is necessary. All practical methods of fighting the injurious insects
must be tried — first on a small scale, and under conditions which the
experimenter can control completely, and then on the larger scale of
actual practice; and these experiments must be repeated under varying
circumstances, until we are sure that all chances of mistake or of acci-
dental coincidence are removed. The whole subject of artificial remedies
for insect depredations, whether topical applications or special modes of
culture, must be gone over critically in this way. So many of the so-
called experiments upon which current statements relating to the value
of remedies and preventives are based have been made by persons
unused to investigation, ignorant of the habits and the transformations
of the insects treated, without skill or training in the estimation of evi-
dence, and failing to understand the importance of verification, that the
whole subject is honeycombed with blunders. Popular remedies for
insect injuries have, in fact, scarcely more value, as a rule, than popular
remedies for disease.
"Observation, record, generalization, experiment, verification —
these are the processes necessary for the mastery of the subject, and
they are the principal and ordinary processes of all scientific research."
The official economic entomologist uses every means to reach the
public for whose benefit he works. Bulletins, circulars and reports,
embodying most serviceable information, are distributed freely where
they will do the most good, and timely advice is disseminated through
newspapers and agricultural journals. An immense amount of corre-
spondence is carried on with individual seekers for help, and personal
influence is exerted in visits to infested localities and by addresses before
agricultural meetings. Special emergencies often tax every resource
of the official entomologist, especially if he is hampered by inadequate
legislative provision for his work. Too often the public, disregarding
the prophetic voice of the expert, refuses to "close the door until the
horse is stolen."
Aside from these emergencies, such as outbreaks of the Rocky Moun-
INSECTS IN RELATION TO MAN 423
tain locust, chinch bug, Hessian fly, San Jose scale and others, the State
or Experiment Station entomologist has his hands full in any State of
agricultural importance; in fact, can scarcely discharge his duties prop-
erly without the aid of a corps of competent assistants.
This chapter would be incomplete without some mention of the
progress of economic entomology in this country, especially since
America is pre-eminently the home of the science. The history of the
science is largely the history of the State and Government entomologists,
for the following account of whose work we are indebted chiefly to the
writings of Dr. Howard, to which the reader is referred for additional
details as well as for a comprehensive review of the status of economic
entomology in foreign countries.
Massachusetts. — Dr. Thaddeus W. Harris, though preceded as a
writer upon economic entomology by William D. Peck, was our pioneer
official entomologist — official simply in the sense that his classic volume
was prepared and published at the expense of the state of Massachu-
setts, first (1841) as a "Report" and later as a "Treatise." The
splendid Flint edition (1862), entitled "A Treatise on Some of the
Insects Injurious to Vegetation," is still "the vade mecum of the working
entomologist who resides in the northeastern section of the country."
Dr. Alpheus S. Packard gave the state three short but useful reports
from 1871 to 1873.
As entomologist to the Hatch Experiment Station of the Massachu-
setts Agricultural College, Prof. Charles H. Fernald issued important
bulletins upon injurious insects, and published in collaboration
with Edward H. Forbush a notable volume upon the gipsy moth.
New York. — Dr. Asa Fitch, appointed in 1854 by the New York State
Agricultural Society, under the authorization of the legislature, was the
first entomologist to be officially commissioned by any state. His
fourteen reports (1855 to 1872) embody the results of a large amount of
painstaking investigation.
In 188 1 Dr. James A. Lintner became state entomologist of New
York. Highly competent for his chosen work, Lintner made every
eft'ort to further the cause of economic entomology, and his thirteen
reports, accurate, thorough and extremely serviceable, rank among the
best. Lintner has had a most able successor in Dr. E. P. Felt, who is
continuing the work with exceptional vigor and the most careful regard
for the entomological welfare of the state. Felt has published at this
writing thirty-eight bulletins (including twenty-one annual reports),
besides important papers on forest and shade-tree insects, and has
424 ENTOMOLOGY
directed the preparation by Needham and his associates of three notable
volumes on aquatic insects.
The Cornell University Agricultural Experiment Station, established
in 1879, has issued many valuable publications upon injurious insects,
written by the master-hand of Professor Comstock or else under his
influence. The studies of Comstock and Slingerland were always made
in the most conscientious spirit and their bulletins — original, thorough
and practical — are models of what such works should be.
More recently, Prof. C. R. Crosby and Prof. G. W. Herrick, of Cor-
nell, have published important contributions to economic entomology.
The Geneva station has issued many excellent entomological
bulletins, the results of investigations by V. H. Lowe, F. A. Sirrine,
H. E. Hodgkiss, P. J. Parrott, and W. J. Schoene.
Illinois. — Mr. Benjamin D. Walsh, engaged in 1867 by the lUinois
State Horticultural Society, published in 1868, as acting state entomolo-
gist, a report in the interests of horticulture — an accurate and
altogether excellent piece of original work. Like many other economic
entomologists he was a prolific writer for the agricultural press and his
contributions, numbering about four hundred, were in the highest degree
scientific and practical.
Walsh was succeeded by Dr. William LeBaron, who published (187 1
to 1874) four able reports of great practical value. In the words of Dr.
Howard, "He records in his first report the first successful experiment
in the transportation of parasites of an injurious species from one locality
to another, and in his second report recommended the use of Paris green
against the canker worm on apple trees, the legitimate outcome from
which has been the extensive use of the same substance against the
codling moth, which may safely be called one of the great discoveries
in economic entomology of late years."
Following LeBaron as state entomologist. Rev. Cyrus Thomas and
his assistants, G. H. French and D. W. Coquillett, produced a creditable
series of six reports (1875 to 1880) as part of a projected manual of the
economic entomology of Illinois.
In 1882 Prof. S. A. Forbes was appointed state entomologist. His
reports and bulletins, based upon the labors of an able corps of assist-
ants, are among the best that have been produced. Of the eighteen
reports issued by Dr. Forbes, those dealing with the chinch bug, San
Jose scale, corn insects and sugar beet insects are especially noteworthy.
The oflEice of state entomologist was discontinued in 191 7, without,
however, any interruption of the entomological work, which is now
INSECTS IN RELATION TO MAX 425
carried on by Dr. Forbes, as director of the Natural History Survey,
with W. P.- Flint as chief entomologist.
Missouri. — Appointed in 1868, Prof. Charles V. Riley published
(1869 to 1877) nine reports as state entomologist. To quote Dr. How-
ard. "They are monuments to the state of Missouri, and more especially
to the man who wrote them. They are original, practical and scientific.
. . . They may be said to have formed the basis for the new economic
entomology of the world." Riley's subsequent work will presently be
spoken of.
Minnesota. — The reports that Dr. O. Lugger issued in Minnesota,
though compiled for the most part, contain much serviceable informa-
tion, presented in a popularly attractive manner. Following Lugger,
F. L. Washburn published several useful reports. The present state
entomologist is Prof. A. G. Ruggles.
New Jersey. — New Jersey has long been active and progressive in
state entomological work. Dr. J. B. Smith, state entomologist from
1894 until his death in 1912. was a most energetic investigator and
prolific writer of useful bulletins and reports. He was succeeded by Dr.
T. J. Headlee, well known for his work in Kansas.
Connecticut. — Dr. W. E. Britton has published twenty reports as
state entomologist. These are of a high degree of excellence, are well
illustrated, and are most useful treatises on the injurious insects of
the state.
Maine. — Dr. C. H. Fernald and Prof. F. L. Harvey formerly
rendered entomological service to the state of Maine. The work is now
in the efficient hands of Dr. Edith M. Patch, an authority on Aphididae,
who has made a reputation for the state by her excellent publications
and those of her co-workers.
California. — The progressive spirit of California has been carried
into the entomological work of the state. Many excellent investiga-
tions, chiefly upon insects affecting citrus plants and the grape, and
upon means of control, have been made by Prof. C. W. Woodworth,
Prof. W. B. Herms, Prof. H. J. Quayle, and Prof. E. O. Essig.
Ohio. — F. M. Webster became known as one of the leading investiga-
tors in economic entomology by his work in Ohio. Since then Prof.
H. A. Gossard and J. S. Houser have made important contributions to
the literature of economic entomology.
Kansas. — Manhattan, Kansas, is a well-known center of entomolog-
ical activity, from which have appeared many important publications on
economic entomology. Prof. G. A. Dean, Dr. J. H. Merrill, and Dr.
426 ENTOMOLOGY
R. C. Smith, with their efficient assistants, are carrying on the work
there. At the University of Kansas, Prof. S. J. Hunter is in charge of
entomological work.
Iowa. — At Ames, Iowa, Prof. H. E. Summers was formerly state
entomologist, followed by R. L. Webster as acting state entomologist,
who was succeeded by Dr. E. D. Ball, now Director of Research of
the U. S. Department of Agriculture. All these men, with Dr. C. P.
Gillette (now of Colorado) and Prof. Herbert Osborn (now of Ohio),
have greatly aided entomological progress by their studies.
Other States. — The states just mentioned are those in which
economic entomology has long been encouraged and developed. In
almost all the other states, however, the value of the science is at present
appreciated. In the following states the work of the entomologists who
are named has been especially noteworthy. Alabama: Dr. W. E. Hinds.
Delaware: Prof. E. D. Sanderson. Prof. C. 0. Houghton. Florida:
Prof. P. H. Rolfs. Prof. H. A. Gossard. Idaho: Prof. J. M. Aldrich.
Indiana: Prof. W. S. Blatchley. Prof. J. J. Davis. Kentucky: Prof.
H. Garman. Louisiana: Prof. H. A. Morgan. Wilmon Newell.
Maryland: W. G. Johnson. Prof. T. B. Symons. Massachusetts:
Prof. C. H. Fernald. Prof. H. T. Fernald. Michigan: Prof. A. J. Cook.
Prof. R. H. Pettitt. Mississippi: Prof. G. W. Herrick. Prof. R. W.
Harned. Missouri: Prof. J. M. Stedman. Montana: Prof. R. A.
Cooley. Nebraska: Prof. L. Bruner. Prof. M. H. Swenk. Nevada:
Prof. S. B. Doten. New Hampshire: Dr. C. M. Weed. Prof. E. D.
Sanderson. Prof. W. C. O'Kane. New Mexico: Prof. C. H. T.
Townsend. Prof. T. D. A. Cockerell. North Carolina: Prof. F.
Sherman, Jr. Oregon: Dr. A. B. Cordley. South Carolina: Prof. A. F.
Conradi. Tennessee: Dr. H. A. Morgan. Washington: Prof. A. L.
Melander. West Virginia: Dr. A. D. Hopkins. Prof. L. M. Peairs.
State Experiment Stations.^The organization of State Agri-
cultural Experiment Stations in 1888, under the Hatch Act, gave
economic entomology an additional impetus. At present at least one
experiment station is in operation in every state and territory; there
being stations in Alaska, Hawaii, Porto Rico, Virgin Islands, and
Guam. These stations, often in connection with state agricultural
colleges, maintain altogether more than two hundred workers in en-
tomology, and have issued a great number of bulletins upon injurious
insects. These publications are extremely valuable as a means of dis-
seminating entomological information, and most of them are based
upon the investigations of their authors.
INSECTS IN RELATION TO MAN 427
While these workers have been conspicuously active in the publica-
tion of their investigations, there are many other station entomologists
and state entomologists who devote themselves entirely to the practical
application of entomological knowledge, and whose work in this respect
is highly important, even though its influence does not extend beyond
the limits of the state.
The U. S. Entomological Commission. — This commission, founded
under a special Act of Congress in 1877 ^o investigate the Rocky Moun-
tain locust, consisted of Dr. C. V. Riley, Dr. A. S. Packard and Rev.
Cyrus Thomas, remained in existence until 188 1, and pubHshed'five
reports and seven bulletins, all of lasting value. The first two reports
form a most elaborate monograph of the Rocky Mountain locust; the
third report includes important work upon the army worm and the
canker worm; the fourth, written by Riley, is an admirable volume on
the cotton worm and boll worm; and the fifth, by Packard, is a useful
treatise on forest and shade-tree insects.
The U. S. Department of Agriculture.- — The first entomological
expert appointed under the general government was Townend Glover,
in 1854. He issued a large number of reports (1863-1877), which ''are
storehouses of interesting and important facts which are too little used
by the working entomologists of to-day," as Howard says. Glover
prepared, moreover, a most elaborate series of illustrations of North
American insects, at an enormous expense of labor, out of all proportion,
however, to the practical value of his undertaking.
Glover was succeeded in 1878 by Riley, whose achievements have
aroused international admiration. He resigned in a year, after writing
a report, and was succeeded by Prof. Comstock, who held office for two
years, during which he wrote two important volumes (published re-
spectively in 1880 and 1881) dealing especially with cotton, orange and
scale insects. His work on scale insects laid the foundation for all our
subsequent investigation of the subject.
Riley, assuming the office of government entomologist, published up
to 1894, "12 annual reports, 31 bulletins, 2 special reports, 6 volumes of
the periodical bulletin Insect Life and a large number of circulars of
information." During his vigorous and enterprising administration
economic entomology took an immense step in advance. The life
histories of injurious insects were studied with extreme care and many
valuable improvements in insecticides and insecticide machinery were
made. One of the notable successes of Dr. Riley and his co-workers,
which has attracted an exceptional amount of public attention, was the
428 ENTOMOLOGY
practical extermination of the fluted scale {Icerya purchasi), which
threatened to put an end to the cultivation of citrus trees in California.
This disaster was averted by the importation from Australia, in 1888, of
a native enemy of the scale, namely the lady-bird beetle Novius ( Vedalia)
cardinalis, which, in less than eighteen months after its introduction
into California, subjugated the noxious scale insect. The United States
has since sent Novius to South Africa, Egypt and Portugal with similar
beneficial results.
The Department of Agriculture succeeded in starting a new and im-
portant industry in California — the culture of the Smyrna fig. The
superior flavor of this variety is due to the presence of ripe seeds, in other
words, to fertilization, and for this it is necessary for pollen of the wild
fig, or ''caprifig," to be transferred to the flowers of the Smyrna fig.
Normally this pollination, or *' caprification," is dependent upon the serv-
ices of a minute chalcid, Blastophaga grossorum, which develops in the
gall-like flowers of the caprifig. The female insect, which in this excep-
tional instance is winged while the male is not, emerges from the gall
covered with pollen, enters the young flowers of the Smyrna fig to ovi-
posit, and incidentally pollenizes them.
After many discouraging attempts, Blastophaga, imported from
Algeria, was established in California, and the new industry has devel-
oped rapidly.
Based upon the foundation laid by Riley, the work of the Bureau
of Entomology has steadily progressed, under the leadership of Dr.
Leland 0. Howard. With a comprehensive and firm grasp of his sub-
ject, alert to discover and develop new possibilities, energetic and
resourceful in management. Dr. Howard has brought the government
work in applied entomology to its present position of commanding
importance. Admirably organized, the Bureau now (1922) requires
the services of 460 employes, 386 of whom are directly engaged in
scientific work.
In the magnitude and importance of its contributions to economic
entomology the Bureau is unapproached by any other organization.
The Bureau of Entomology has always secured the services of the
best entomologists avaflable, and its staff of experts includes many of
the leading entomologists of the world. Those in charge of the work
are as follows: Dr. L. O. Howard, entomologist and chief of bureau.
C. L. Marlatt, entomologist and assistant chief of bureau. W. D.
Hunter, southern field crop insect investigations. W. R. Walton,
cereal and forage insect investigations. Prof. A. L. Quaintance, decidu-
INSECTS IN RELATION TO MAN 429
ous-fruit insect investigations, tropical and subtropical fruit insect
investigations. C. L. Marlatt, investigations of the Mediterranean
and other fruit flies. Dr. F. H. Chittenden, truck-crop insect investiga-
tions. E. A.. Back, stored-product insect investigations. Dr. A. D.
Hopkins, forest insect investigations. Dr. L. O. Howard, W. D. Hun-
ter, and J. L. Webb, investigations of insects affecting the health of
man and animals. Dr. E. F. Phillips, investigations in bee culture.
A. F. Burgess, gipsy moth and brown-tail moth investigations.
The U. S. Department of Agriculture publishes annually a List of
Workers in Subjects Pertaining to Agriculture, which contains the names
of all the entomological workers in the Department of Agriculture, in
State Agricultural Colleges and in Experiment Stations.
Canada. — The development of economic entomology in Canada
was due largely to the efforts of Dr. James Fletcher, of the Dominion
Experimental Farms, Ottawa, whose annual reports and other writings
were of exceptional value. His work was furthered in every way by
the "eminent director of the experimental farms system. Dr. William
Saunders, himself a pioneer in economic entomology in Canada and the
author of one of the most valuable treatises upon the subject that has
ever been published in America." Dr. Fletcher was Government ento-
mologist from 1884 until his death, in 1908. Dr. C. Gordon Hewitt,
who was appointed Dominion entomologist in 1909, made in ten years a
brilliant record in public service. His remarkable work was cut short
by his death in February, 1920. In October, 1920, Arthur Gibson was
made Dominion entomologist. He is well fitted by ability and experience
to maintain the standard of excellence set by his eminent predecessors.
Outside of the government work, entomology in Canada centers
around the Entomological Society of Ontario, whose excellent publica-
tions, sustained by the government, are of great scientific and educa-
tional importance. In addition to its annual reports, this society
issues the Canadian Entomologist, one of the leading serials of its
kind, edited for many years by its founder, the Rev. C. J. S. Bethune,
whose devoted services have been appreciated by every entomologist.
The Association of Official Economic Entomologists.— Organ-
ized in 1889 by a few energetic workers, this association has had a rapid
and healthy growth and now numbers among its members all the leading
economic entomologists of America and a large number of foreign work-
ers. The annual meetings of the association impart a vigorous stimulus
to the individual worker and tend to promote a well-balanced develop-
ment of the science of economic entomology.
LITERATURE
The literature on entomological subjects now numbers about 150,000 titles. The
works listed below have been selected chiefly on account of their general usefulness and
accessibility. Works incidentally containing important bibliographies of their special
subjects are designated each by an asterisk — *.
BIBLIOGRAPHICAL WORKS
Hagen, H. A. Bibliotheca Entomologica. 2 vols. Leipzig, 186 2- 1863. Covers the entire
literature of entomology up to 1862,
Englemann, W. Bibliotheca Historico-Naturalis. i vol. Leipzig, 1846. Literature
1 700-1846.
Carus, J. v., and Englemann, W. Bibliotheca Zoologica. 2 vols. Leipzig, 186 1. Litera-
ture, I 846-1 860.
Taschenberg, O. Bibliotheca Zoologica. 5 vols. Leipzig, 1887-1899. Vols. 2 and 3,
entomological literature, 1861-1880.
The Zoological Record. London. Annually since vol. for 1864.
Catalogue of Scientific Papers, Royal Society. London. Since 1868.
Zoologischer Anzeiger. Leipzig. Fortnightly since 1878. Bibliographica Zoologica,
annual volumes since 1896.
Concilium Bibliographictmi. Zurich. Card catalogue of current zoological literature
since 1896.
Archiv fiir Naturgeschichte. Berlin. Annual summaries since 1835.
Journal of the Royal Microscopical Society. London. Summaries of the most important
works, beginning 1878.
Zoologischer Jahresbericht. Leipzig. Yearly summaries of literature since 1879.
Zoologisches Centralblatt. Leipzig. Reviews of more important literature since 1895.
Psyche. Cambridge, Mass. Records of American literature. Also earlier records,
beginning 1874.
Entomological News. — Philadelphia, 1890 to date. Records of current literature.
BibUography of the more important contributions to American Economic Entomology.
8 parts. Pts. 1-5 by S. Henshaw; pts. 6-8 by N. Banks. 1318 pp. Washington,
1889-1905.
Banks, N. 1917. Index to the Literature of American Economic Entomology. Jan. i,
1905 to Dec. 31, 1914. 5 + 323 pp. Amer. Assoc. Econ. Ent. Melrose Highlands,
Mass.
Colcord, M. 1921. Index II to the Literature of American Economic Entomology. Jan.
1, 1915 to Dec. 21, 1919. 4 + 388 pp. Amer. Assoc. Econ. Ent. Melrose High-
lands, Mass.
Review of Applied Entomology. 1913 to date. Series A: Agricultural. Series B : Medical
and Veterinary. Imperial Bureau of Entomology. London. Dulau & Co., Ltd.
Reviews of current literature.
Catalogue of Scientific Serials, 1633-1876. S. H. Scudder. Cambridge, Mass. Harvard
University, 1879.
A Catalogue of Scientific and Technical Periodicals, 1665-1895. H. C. Bolton. Wash-
ington, Smithsonian Institution, 1897.
430
LITERATURE 43 1
A List of Works on North American Entomology. N. Banks. Bull. U. S. Dept. Agric,
Bur. Ent., no. 81 (n.s.), 120 pp. Washington, 1910.
GENER.\L ENTOMOLOGY
Kirby, W., and Spence, W. 1822-26. An Introduction to Entomology. 4 vols. 36 +
2413 pp., 30 pis. London.
Burmeister, H. 1832-55. Handbuch der Entomologie. 2 vols. 28 + 1746 pp., 16 taf.
Trans, of Band i : 1836. W. E. Shuckard. A Manual of Entomology. 12 +
654 pp., 32 pis. London.
Westwood, J. O. 1839-40. An Introduction to the Modern Classification of Insects.
2 vols. 23 + 620 pp., 133 figs. London.
Graber, V. 1877-79. Die Insekten. 2 vols. 8 + 1008 pp., 404 figs. MUnchen.
Miall, L. C, and Denny, A. 1886. The Structure and Life-History of the Cockroach.
6 + 224 pp., 125 figs. London, Lovell Reeve & Co.; Leeds, R. Jackson.
Comstock, J. H. 1888. An Introduction to Entomology. 4 + 234 pp., 201 figs. Ithaca,
N. Y.
Kolbe, H. J. 1889-93. Einfuhrung in die Kenntnis der Insekten. 12 + 709 pp., 324 figs.
Berlin. F. Diimmler.*
Packard, A. S. 1889. Guide to the Study of Insects. Ed. 9. 12 + 715 pp., 668 figs.,
15 pis. New York. Henry Holt & Co.
Hyatt, A., and Arms, J. M. 1890. Insecta. 23 + 300 pp., 13 pis., 223 figs. Boston.
D. C. Heath & Co.*
Kirby, W. F. 1892. Elementary Text-Book of Entomology. Ed. 2. 8 -t- 281 pp., 87 pis.
London. Swan Sonnenschein & Co.
Comstock, J. H. and A. B. 1895. A Manual for the Study of Insects. 7 + 701 pp.,
797 figs., 6 pis. Ithaca, N. Y. Comstock Pub. Co.
Sharp, D. 1895, 1901. Insects. Cambr. Nat. Hist., vols. 5, 6. 12 -f 1130 pp., 618 figs.
London and New York. Macmillan & Co.*
Comstock, J. H. 1897, 1901. Insect Life. 6 -|- 349 PP-, 18 pis., 296 figs. New York.
D. Appleton & Co.
Packard, A. S. 1898. A Text-Book of Entomology. 17 -f 729 pp., 654 figs. New York
and London. The Macmillan Co.*
Carpenter, G. H. 1899. Insects; their Structure and Life. 11 + 404 pp., 184 figs.
London. J. M. Dent & Co.*
Packard, A. S. 1899. Entomology for Beginners. Ed. 3. 16 -f 367 pp., 273 figs. New
York. Henry Holt & Co.*
Howard, L. O. 1901. The Insect Book. 27 -|- 429 pp., 48 pis., 264 figs. New York.
Doubleday, Page & Co.
Hxmter, S.J. 1902. Elementary Studies in Insect Life. 18 -f 344 pp., 234 figs. Topeka.
Crane & Co.
Henneguy, L. F. 1904. Les Insectes. Morphologic, Reproduction, Embryogenie.
18 4- 804 pp., 622 figs., 4 pis. Paris. Masson et Cie. Contains more than two
thousand references.*
Kellogg, V. L. 1905. American Insects. 7 + 674 pp., 13 pis., 812 figs. New York.
Henry Holt & Co.
Berlese, A. 1909-13. Gli Insetti. Vol. i, 10 + 1004 pp., 1292 figs., 10 pis. Vol. 2,
240 pp. 233 figs. Milan. Contains exhaustive bibliographies.*
Sanderson, E. D., and Jackson, C. F. 1912. Elementary Entomology, 5 + 372 pp.,
496 figs. Boston and New York. Ginn & Co.
Sanderson, E. D., and Peairs, L. M. 1917. School Entomology. 7 + 356 pp., 233 figs.
New York. John Wiley & Sons, Inc.
432 ENTOMOLOGY
Lutz, F. E. 1918. Fieldbook of Insects. 9 + 5C9 pp., 101 pis. New York & London.
G. P. Putman's Sons.*
Comstock, J. H. 1920. An Introduction to Entomology. Second Ed. 18 + 220 pp.,
220 figs. Ithaca, N. Y. Comstock Pub. Co.*
PHYLOGENY AND CLASSIFICATION
Kirby, W., and Spence, W. 1822-26 An Introduction to Entomologj-. 4 vols. 36 +
2413 pp., 30 pis. London.
Burmeister, H. 1832. Handbuch der Entomologie. 2 vols. 28 + 1746 pp., 16 taf.
Berlin. Translation of Band i : 1836. W. E. Shuckard. A Manual of Entomol-
ogy. 12 + 654 pp., 32 pis. London. Contains useful synopses of the older
systems of classification.
Westwood, J. O. 1839-40. An Introduction to the Modern Classification of Insects.
2 vols. 23 + 620 pp., 133 figs. London.
Packard, A. S. 1873. Our Common Insects. 255 pp., 268 figs. Boston. Estes &
Lauriat.
Lubbock, J. 1874. On the Origin and Metamorphoses of Insects. 16 + 108 pp., 63 figs.,
6 pis. London. Macmillan & Co.*
Mayer, P. 1876. Ueber Ontogenie und Phylogenie der Insekten. Jenais. Zeits.
Naturw., bd. 10, pp. 125-221, taf. 6-6c.
Haase, E. 1881. Beitrag zur Phylogenie und Ontogenie der Chilopoden. Zeits. Ent.
Breslau, bd. 8, heft 2, pp. 93-115.
Packard, A. S. 1881. Scolopendrella and its Position in Nature. Amer. Nat., vol. 15,
pp. 698-704, fig. I.
Brauer, F. 1885. Systematisch-zoologische Studien. Sitzb. Akad. Wiss., Wien, bd. 91,
pp. 237-413.*
Grassi, B. 1885. I progenitori degli Insetti e dei Miriapodi. — Morfologia delle Scolo-
pendreUe. Atti. Accad. Torino, t.. 21, pp. 48-50.
Glaus, C. 1887. On the Relations of the Groups of Arthropoda. Ann. Mag. Nat. Hist.,
ser. 5, vol. 19, p. 396.
Haase, E. 1889. Die Abdominalanhange der Insekten mit Beriicksichtigung der Myrio-
poden. Morph. Jahrb., bd. 15, pp. 33i-435> taf. 14, 15.
Femald, H. T. 1890. The Relationships of Arthropods. Studies Biol. Lab. Johns
Hopk. Univ., vol. 4, pp. 431-513, pis. 48-50.
Hyatt, A., and Arms, J. M. 1890. Insecta. 23 + 300 pp., 13 pis, 223 figs. Boston.
D. C. Heath & Co.*
Cholodkowsky, N. 1892. On the Morphology and Phylogeny of Insects. Ann. Mag.
Nat. Hist., ser. 6, vol. 10, pp. 429-451.
Grobben, C. 1893. A Contribution to the Knowledge of the Genealogy and Classification
of the Crustacea. Ann. Mag. Nat. Hist., ser. 6, vol. 11, pp. 440-473. Trans.
from Sitzb. Akad. Wiss. Wien, math.-nat. CI., bd. loi, heft 2, pp. 237-274, taf. i.
Hansen, H. J. 1893. A Contribution to the Morphology of the Limbs
and Mouth-parts of Crustaceans and Insects. Ann. Mag. Nat. Hist., ser. 6,
vol. 12, pp. 417-434. Trans, from Zool. Anz., jhg. 16, pp. 193-198, 201-212.
Pocock, R. I. 1893. On some Points in the Morphology of the Arachnida (s. s.) with
Notes on the Classification of the Group. Ann. Mag. Nat. Hist., ser. 6. vol. 11,
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Bernard, H. M. 1894. The Systematic Position of the Trilobites. Quart. Journ. Geol.
Soc. London, vol. 50, pp. 411-434, figs. 1-17.
Kenyon, F. C. 1895. The Morphology and Classification of the Pauropoda, with Notes on
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LITERATURE
433
Schmidt, P. 1896. Beitrage zur Kenntnis der niederen Myriapoden. Zeits. wiss. Zool.,
bd. 5Q, pp. 436-510, taf. 26, 27.
Wagner, J. 1895. Contributions to the Phylogeny of the Arachnida. Ann. Mag. Nat.
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pp. 123-156.
Sedgwick, A. 1895. Peripatus. Camb. Nat. Hist., vol. 5, pp. 1-26, figs. 1-14.
Sinclair, F. G. 1895. Myriapoda. Camb. Nat. Hist., vol. 5, pp. 27-80, figs. 15-46.
Sharp, D. 1895,1901. Insects. Camb. Nat. Hist., vols. 5, 6. 12 + 1130 pp., 618 figs.
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Comstock, J. H. and A. B. 1895. A Manual for the Study of Insects. 7 + 70: pp., 797
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Heymons, R. 1896. Zur Morphologic der Abdominalanhange bei den Insecten. Morph.
Jahrb., bd. 24, pp. 178-204, i taf.
Heymons, R. 1897. Mittheilungen iiber die Segmentierung und den Korperbau der
IMyriopoden. Sitzb. Akad. Wiss., Berhn, bd. 40, pp. 915-923, 2 figs.
Hansen, H. J., and Sorensen, W. 1897. The Order Palpigradi Thor. and its Relation-
ship to the Arachnida. Ent. Tidsk., arg. 18, pp. 223-240, pi. 4.
Packard, A. S. 1898. A Text-Book of Entomology. 17 -+- 729 pp., 654 figs. New York
and London. The Macmillan Co.*
Packard, A. S. 1899. Entomology for Beginners. Ed. 3. 16 + 367 pp., 273 figs. New
York. Henry Holt & Co.*
Von Zittel, K. A. 1900,1902. Te.xt-Book of Palaeontology. 2 vols. Trans. C.R.East-
man. London and New York. Macmillan & Co.*
Folsom, J. W. 1900. The Development of the Mouth Parts of Anurida maritima Guer.
Bull. Mus. Comp. Zool., vol. 36, pp. 87-157, pis. 1-8.*
Hansen, H. J. 1902. On the Genera and Species of the Order Pauropoda. Vidensk.
Medd. Naturh. Foren. Kjobenhavn (1901), pp. 323-424, pis. 1-6.
Carpenter, G. H. 1903. On the Relationships between the Classes of the Arthropoda.
Proc. R. Irish Acad., vol. 24, pp. 320-360, pi. 6.*
Enderlein, G. 1903. Ueber die Morphologic, Gruppierung und systematische SteUung
der Corrodentien. Zool. Anz., bd. 26, pp. 423-437, 4 figs.
Hansen, H. J, 1903. The Genera and Species of the Order Symphyla. Quart. Journ.
Micr. Sc, vol. 47 (n. s.), pp. i-ioi, pis. 1-7.-
Packard, A. S. 1903. Hints on the Classification of the Arthropoda; the Group, a Poly-
phyletic One. Proc. Amer. Phil. Soc, vol. 42, pp. 142-161.
Lankester, E. R. 1904. The Structure and Classification of the Arthropoda. Quart.
Journ. Micr. Sc, vol. 47 (n. s.), pp. 523-582, pi. 42. (From Encyc. Brit., ed. 10.)
Bomer, C. 1904. Zur Systematik der Hexapoden. Zool. Anz., bd. 27, pp. 511-533,
figs. 1-4.*
Bouvier, E. L. 1905, 1907. Monographic des Onychophores. Ann. Sc. nat. Zool.,
ser. 9, t. 2, pp. 1-383, 140 figs., 13 pis.; t. 5, pp. 61-318, figs. 141-191.*
Carpenter, G. H. 1905. Notes on the Segmentation and Phylogeny of the Arthropoda,
with an Account of the Maxillae in Polyxenus lagurus. Quart. Journ. Micr. Sc,
vol. 49, pt. 3, pp. 469-491, pi. 28.*
Silvestri, F. 1907. Descrizione di un novo genere d'insetti apteygoti. *^11. Lab. Zool.
gen. agr., vol. i, pp. 296-311, 18 figs.
Handlirsch, A. 1908. Die Fossilen Insekten und die Phylogenie der Rezenten Formen.
49 + 1430 pp., 14 figs., 51 pis., etc. Leipzig. W. Engelmann.*
Sedgwick, A. 1908. The Distribution and Classification of the Onychophora. Quart.
Journ. Micr. Sc, vol. 52 (n. s.), pp. 379-406, figs. 1-13.*
Berlese, A. 1909. Monografia dei Myrientomata. Redia, vol. 6, pp. 1-182, 17 pis., 14
figs.
434 ENTOMOLOGY
Pierce, W. D. 1909. A Monographic Revision of the Twisted Winged Insects comprising
the Order Strepsiptera Kirby. Bull. U. S. Nat. Mus. No. 66, pp. 12 + 232, figs.
1-3, pis. 1-15.*
Schepotieff, A. 1909. Studien iiber niedere Insecten. Zool. Jahrb., Abt. Syst. Geogr.
Biol., bd. 28, pp. 121-138, tab. 3-5.
Bomer, C. 1910. Die phylogenetische Bedeutung der Protura. Biol. Zentralbl. bd. 30,
pp. 633-641.
Prell, H. 1911-12. Beitrage zur Kenntniss der Protura. Zool. Anz., bd. 38, pp. 185-193;
bd. 39, pp. 357-365; bd. 40, 33-50-
Rimsky-Korsakow, M. 1911. Ueber die systematische Stellung der Protura Silvestri.
Zool. Anz., bd. 37, pp. 164-168, i fig.
Comstock, J. H. 1912. The Spider Book. 13 + 721 pp., 770 figs. New York. Double-
day, Page & Co.*
Handlirsch, A. 1913, 1920. Aus der Geschichte der Entomologie. Also chapters on
literature, technique, taxonomy, etc. In Schroder: Handbuch der Entomologie,
bd. 3, pp. 1-116, figs. 1-51.*
Silvestri, F. 1913. Descrizione di un nuovo ordine di insetti. Boll. Lab. Zool. gen. agr.,
vol. 7, pp. 193-209, 13 figs.
Williams, C. B. 1913. A Summary of the Present Knowledge of the Protura. Ento-
mologist, vol. 46, pp. 225-232, figs. I, 2.*
Walker, E. M. 1914. . A New Species of Orthoptera, forming a New Genus and Family.
Can. Ent., vol. 46, pp. 93-99, pi. 6.
Banks, N. 1915. The Acarina or Mites. Rept. U. S. Dept. Agric, no. 108, 153 pp.,
294 figs.*
Brues, C. T., and Melander, A. L. 1915. Key to the Families of North American Insects.
7 -f 140 pp., 18 pis. Boston, Mass. and Pullman, Wash. Pub. by the authors.
Crampton, G. C. 1915. The Thoracic Sclerites and the Systematic Position of Gryllo-
blatta campodeiformis Walker, a Remarkable Annectent " Orthopteroid " Insect.
Ent. News, vol. 26, pp. 337-350, pi. 13.
Crampton, G. C. 1916. The Orders and Relationships of Apterygotan Insects. Journ.
N. Y. Ent. Soc, vol. 24, pp. 267-301.*
Crampton, G. C. 1917. A Phylogenetic Study of the Terminal Abdominal Segments and
Appendages in Some Female Apterygotan and Lower Pterygotan Insects. Journ.
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Crampton, G. C. 1917. A Phylogenetic Study of the Lateral Head, Neck and Prothoracic
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Caudell, A. N. 1918. Zorotypus hubbardi, a New Species of the Order Zoraptera from
the U. S. Can. Ent.,vol. 50, pp. 375-381.
Pierce, W. D. 1918. The Comparative Morphology of the Order Strepsiptera together
with Records and Descriptions of Insects. Proc. U. S. Nat. Mus., vol. 54, pp.
391-501, pis. 64-78,*
Brues, C. T. 1919. The Classification of Insects on the Characters of the" Larva and
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Crampton, G. C. 1919. Notes on the Phylogeny of the Orthoptera. Ent. News, vol.
30, pp. 42-48; 64-72.
Crampton, G. C. 1919. The Evolution of Arthropods and their Relatives, with especial
Reference to Insects. Amer. Nat., vol. 53, pp. 143-179.*
Crampton, G. C. 1919. Notes on the Ancestry of the Diptera, Hemiptera, and other
Insects related to the Neuroptera. Trans. Ent. Soc. London, pp. 93-118, 2 figs.
Walker, E. M. 1919. The Terminal Abdominal Structures of Orthopteroid Insects: a
Phylogenetic Study. Ann. Ent. Soc. Amer., vol. 12, pp. 267-326, pis. 20-28.
LITERATURE 435
Caudell, A. N. 1920. Zoraptera not an Apterous Order. Proc. Ent. Soc. Washington,
vol. 22, pp. 84-97, pi. 6.
Crampton, G. C. 1920. Some Anatomical Details of the Remarkable Winged Zorapteron.
Zorotypus hubbardi Caudell, with Notes on its Relationships. Proc. Ent. Soc.
Washington, vol. 22, pp. 98-106, pi. 7.
Crampton, G. C. 1920. A Comparison of the External Anatomy of the Lower Lepidop-
tera and Trichoptera from the Standpoint of Phylogeny. Psyche, vol. 27, pp.
23-44, pi. 4.*
Crampton, G. C. 1920. Notes on the Lines of Descent of Lower Winged Insects. Psyche,
vol. 27, pp. 116-127, 6 figs.
Crampton, G. C. 1921. Preliminary Note on the interpretation of Insectan and Myrio-
podan structures through a comparison with the structures of Crustacea. Trans.
Ent. Soc. London, pp. 340-346.
Crampton, G. C. 1921. A Further Comparison of the Wings of Zoraptera, Psocids, and
Aphids, from the Standpoint of Phylogeny. Can. Ent., vol. 53, pp. 110-117,
pl. 3-*
Ewing, H. E. 1921. A Second Nearctic Species of Protura, Accrcntuliis barbcri, New
Species. Ent. News, vol. 32, pp. 239-241.
Ewing, H. E. 1921. New Genera and Species of Protura. Proc. Ent. Soc. Washington,
vol. 23, pp. 193-202, pl. 16.
Handlirsch, A. 1921. Philogenie oder Stammesgeschichte. In Schroder: Handbuch
der Entomologie, bd. 3, pp. 307-368, figs. 238-289.
Crampton, G. C. 1922. A Comparison of the First Maxillae of Apterygotan Insects and
Crusta,cea from the Standpoint of Phylogeny. Proc. Ent. Soc. Washington, vol.
24, pp. 65-82, figs. 1-6, pis. 8, 9.*
Walker, E. M. 1922. The Terminal Structures of Orthopteroid Insects: a Phylogenetic
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GENERAL ANATOMY
De Reatmiur, R. A. F. 1734-42. Memoires pour servir a I'histoire des insectes. 7 vols.
Paris.
Lyonet, P. 1762. Traite anatomique de la Chenille, qui ronge le Bois de Saule. Ed. 2.
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Straus-Durckheim, H. 1828. Considerations generales sur I'anatomie comparee des
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Newport, G. 1839. Insecta. Todd's Cyclopaedia Anat. Phys., vol. 2, pp. 853-994, figs.
329-439-
Viallanes, H. 1882. Recherches sur I'histologie des insectes. Ann. Sc. nat. ZooL, ser. 6,
t. 14, pp. 1-348, pis. 1-18.
Miall, L. C, and Deimy, A. 1886. The Structure and Life-history of the Cockroach.
6 + 224 pp., 125 figs. London, Lovell Reeve & Co.; Leeds, R. Jackson.
Schaeffer, C. 1889. Beitrage zur Histologie der Insekten. Zool. Jahrb., Morph. Abth.,
bd. 3, pp. 611-652, taf. 29, 30.
Lowne, B. T. 1890-92. The Anatomy, Physiology, Morphology and Development of the
Blow-fly (Calliphora erythrocephala) . A Study in the Comparative Anatomy and
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Lang, A. 1891. Text-Book of Comparative Anatomy. Trans, by H. M. and M. Bernard.
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Comstock, J. H., and Kellogg, V. L. 1899. The Elements of Insect Anatomy. Rev. ed.
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436 ENTOMOLOGY
Hewitt, C. G. 1907-9. The Structure, Development, and Bionomics of the House-fly,
Musca domesticaLinn. Quart. Journ. Micr. Sc, vol. 51 (n. s.), pp. 395-448, pis.
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Snodgrass, R. E. 1910. The Anatomy of the Honey Bee. Bull. U. S. Dept. Agr.,
Bur. Ent., Tech. Ser. No. 18. 162 pp., 57 figs.*
Schroder, C. 1912-21. Handbuch der Entomologie. Bd. i, 3, Lief. 1-7, 928 pp., 716
figs. Jena. Gustav Fischer.*
Jordan, H. 1913. Vergleichende Physiologic wirbelloser Tiere. Bd. i, pp. 22 + 738,
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HEAD AND APPENDAGES
Burgess, E. 1880. Contributions to the Anatomy of the Milk-weed Butterfly (Danais
archippus Fabr.). Anniv. Mem. Bost. Soc. Nat. Hist., 16 pp., 2 pis.
Ditnmock, G. 1881. The Anatomy of the Mouth Parts and of the Sucking Apparatus of
some Diptera. 50 pp., 4 pis. Boston. A. Williams & Co.*
Kraepelin, K. 1883. Zur Anatomic und Physiologic des Russels von Musca. Zeits. wiss.
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Wedde, H, 1885. Beitrage zur Kenntniss des Rhynchotenriissels. Archiv Naturg. , jhg.
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Breithaupt, P. F. 1886. Uebcr die Anatomic und die Functioncn der Bienenzunge.
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Folsom, J, W, 1900. The Development of the Mouth Parts of Anurida maritima Guer.
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Comstock, J. H., and Kochi, C. 1902. The Skeleton of the Head of Insects. Amer.
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Kellogg, V. L. 1902. The Development and Homologies of the Mouth Parts of Insects.
Amer. Nat., vol. 36, pp. 683-706, figs. 1-26.
Meek, W. J. 1903. On the Mouth Parts of the Hcmiptera. Kansas Univ. Sc. Bull., vol.
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Holmgren, N. 1904. Zur Morphologic des Insektenkopfes. Zeits. wiss. Zool., bd. 76,
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LITERATURE 437
Demoll, R. 1908. Die Mundteile der solitiiren Apiden. Zeits. wiss. Zool., bd. 91, pp.
1-5 1, taf. I, 2, II figs.
Demoll, R. 1909. Die Mundteile der Vespen, etc. Zeits. wiss. Zool, bd. 92, pp. 187-209,
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Wesche, W. 1909. The Mouth-parts of the Nemocera, etc. Journ. Roy. Micr. Soc,
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Tower, D. G. 1914. The Mechanism of the Mouth Parts of the Squash Bug, Anasa
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Peterson, A. 1915. Morphological Studies of the Head and Mouth Parts of the Thy-
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Peterson, A. 1916. The Head-Capsule and Mouth-Parts of Diptera. 111. Biol. Monogr.,
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Peacock, A. D. 1918. The Structure of the Mouth Parts and Mechanism of Feeding in
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Crampton, G. C. 1921. The Sclerites of the Head, and the Mouth Parts of Certain.
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Crampton, G. C. 1921. The Origin and Homologies of the So-called "Superlinguae" or
" Paraglossae " (Paragnaths) of Insects and Related Arthropods. Psyche, vol.
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Crampton, G. C. 1922. The Derivation of Certain Types of Head Capsule in Insects
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THORAX AND APPENDAGES; LOCOMOTION
Pettigrew, J. B. 1874. Animal Locomotion. 13 -f 264 pp., 130 figs. New Yoric
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Dahl, F. 1884. Beitrage zur Kenntnis des Baues und der Funktionen der Insektenbeine.
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Amans, P. C. 1888. Comparaisons des organes de la locomotion aquatique. Ann. Sc.
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Ockler, A. 1890. Das Krallenglied am Insektenfuss. Archiv Naturg., jhg. 56, bd. i,
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438 ENTOMOLOGY
Hoffbauer, C. 1892. Beitrage zur Kenntnis der Insektenfliigel. Zeits. wiss. Zool., bd.
54, pp. 579-630, taf. 26, 27, 3 figs.*
Sptiler, A. 1892. Zur Phylogenie und Ontogenie des Fliigelgeader der Schmetterlinge.
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Comstock, J, H. 1893. Evolution and Taxonomy. Wilder Quarter-Century Book,
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Marey, E. J. 1895. Movement. 15 + 323 pp., 204 figs. New York. D. Appleton
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Snodgrass, R. E. 1908. A Comparative Study of the Thorax in Orthoptera, Euplex-
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Crampton, G. C. 1916. The Phylogenetic Origin and the Nature of the Wings of Insects
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Martin, J. F. 1916. The Thoracic and Cervical Sclerites of Insects. Ann. Ent. Soc.
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pp. 111-116.
Tillyard, R. J. 1919. The Panorpoid Complex. Part 3:— The Wing- Venation. Proc.
Linn. Soc. New South Wales, vol. 44, pt. 3, pp. 533-718, figs. 35-112, pis.
3I--35-*
Prochnow, O. 1921. Mechanik des Insektenfluges. In Schroder: Handbuch der Ento-
mologie, bd. i pp. 534-560, figs. 1-25.
LITERATURE
ABDOMEN AND APPENDAGES
439
Dewitz, H. 1875. Ueber Bau und Entwickelung des Stachels und der Legescheide einiger
Hymenopteren und der grunen Heuschrecke. Zeits. wiss. Zool., bd. 25, pp. 174-
200, taf. 12, 13.
Adler, H. 1877. Lege-Apparat und Eierlegen der Gallwespen. Deuts. ent. Zeits., jhg.
21, pp. 305-332, taf. 2.
Dewitz, H. 1877. Ueber Bau und Entwickelung des Stachels der Ameisen. Zeits. wiss.
Zool., bd. 28, pp. 527-556, taf. 26.
Goossens, T. 1887. Les pattes des Chenilles. Ann. Soc. ent. France, s^r. 6, t. 7, pp.
385-404, pi. 7.
Graber, V. 1888. Ueber die Polypodie bei Insekten-Embryonen. ' Morph. Jahrb., bd. 13,
pp. 586-615, taf. 25, 26.
Haase, E. 1889. Ueber Abdominalanhange bei Hexapoden. Sitzb. Gesell. naturf.
Freunde, pp. 19-29.
Haase, E, 1889. Die Abdominalanhange der Insekten mit Beriicksichtigung der Myri-
opoden. Morph. Jahrb., bd. 15, pp. 331-435, taf. 14, 15.
Carlet, G. 1890. Memoire sur le venin et I'aiguillon de I'abeille. Ann. Sc. nat. Zool., ser.
7, t. 9, pp. 1-17, pl- I-
Packard, A. S. 1890. Notes on some points in the external structure and phylogeny of
Lepidopterous larvae. Proc. Bost. Soc. Nat. Hist., vol. 25, pp. 82-114, pis.
I, 2.
Wheeler, W. M. 1890. On the Appendages of the first abdominal Segment of embryo
Insects. Trans. Wis. Acad. Sc, vol. 8, pp. 87-140, pis. 1-3.*
Escherich, K. 1892. Die biologische Bedeutung der Genitalanhange der Insekten. Verb.
zool.-bot. Ges. Wien, bd. 42, pp. 225-240, taf. 4.
Graber. V. 1892. Ueber die morphologische Bedeutung der Abdominalanhange der
Insekten-Embryonen. Morph. Jahrb., bd. 17, pp. 467-482,
Escherich, K. 1894. Anatomische Studien iiber das mannliche Genital-system der Cole-
opteren. Zeits. wiss. Zool., bd. 57, pp. 620-641, taf. 26, 3 figs.
Verhoeff, C. 1894. Vergleichende Untersuchungen iiber die Abdominalsegmente der
weiblichen Hemiptera-Heteroptera und Homoptera. Verb. nat. Ver. Bonn, jhg.
50, pp. 307-374-
HeymoDS, R. 1895. Die Segmentirung des Insectenkorpers. Anh. Abh. Preuss. Akad.
"Wiss. Berlin, 39 pp., i taf.
Heymons, R. 1895. Die Embryonalentwickelung von Dermapteren und Orthopteren
unter besonderer Beriicksichtigung der Keimblatterbildung. 136 pp., 12 taf., ^^
figs. Jena.
Pejrtoureau, S. A. 1895. Contribution a I'etude de la morphologie de I'armure genitale
des Insectes. 248 pp., 22 pis., 43 figs. Paris.
Verhoeff, C. 1895. Cerci und Styli der Tracheaten. Ent. Nachr., jhg. 21, pp. 166-168.
Heymons, R. 1896. Grundziige der Entwickelung und des Korperbaues von Odonaten
und Ephemeriden. Anh. Abh. Akad. Wiss. Berlin, pp. 66, 2 taf.
Heymons, R. 1896. Zur Morphologie des Abdominalanhange bei den Insekten. Morph.
Jahrb., bd. 24, pp. 178-204, taf. i.
Verhoeff, C. 1896. Zur Morphologie der Segmentanhange bei Insecten und Myriopoden.
Zool. Anz., bd. 19, pp. 378-383, 385-388.
Janet, C. 1897. Limites morphologiques des anneaux post-cephaliques et Musculature
des anneau\ post-thoraciques chez la Myrmica rubra. Note 16. 35 pp., 10 figs.
Lille.
Verhoeff, C. 1897. Bemerkungen iiber abdominale Korperanhange bei Insecten und
Myriopoden. Zool. Anz., bd. 20, pp. 293-300.
440 ENTOMOLOGY
Janet, C. 1898. Aiguillon de la Myrmica rubra. Appareil de fermeture de la glande a
venin. Note i8. 27 pp., 3 pis. Paris.
Zander, E. 1903. Beitrage zur Morphologic der mannlichen Geschlechtsanhange der
Lepidopteren. Zeits. wiss. Zool., bd. 74, pp. 557-615, taf. 29, figs. 1-15.*
Verhoeff, K. W. 1917. Zur vergleichenden Morphologic des Abdomens der Colcoptcrcn,
etc. Zeits. wiss. Zool., bd. 117, pp. 130-204, 12 figs., 2 pis.*
Crampton, G. C. 1918. A Phylogcnctic Study of the Terminal Abdominal Structures
and Genitalia of Male Apterygota, Ephemcrids, Odonata, Plecoptcra, Neurop-
tera, Orthoptcra, and Their AUies. Bull. Brooklyn Ent. Soc, vol. 13, pp. 49-68,
pis. 2-7.*
Newell, A. G. 1918. The Comparative Morphology of the Genitalia of Insects. Ann.
Ent. Soc. Am'er., vol. 11, pp. 109-156, pis. 4-17.*
Crampton, G. C. 1920. A Comparison of the Genitalia of Male Hymenoptera, Mecop-
tera, Xeuroptera, Diptera, Trichoptera, Lepidoptera, Homoptera, and Strepsip-
tera, with Those of Lower Insects. Psyche, vol. 27, pp. 34-44, pis. 2-4.*
Crampton, G. C. 1920. Remarks on the Basic Plan of the Terminal Abdominal Struc-
tures of the Males of Winged Insects. Can. Ent., vol. 52, pp. 178-183, pi. 6.
Crampton, G. C. 1921. A Comparison of the Terminal Abdominal Structures of Insects
and Crustacea. Ent. News, vol. 32, pp. 257-264, pi. 5.
INTEGUMENT
Candeze, E. 1874. Les moyens d'attaque et de defense chez les Insectes. Bull. Acad.
roy. Belgique, ser. 2, t. 38, pp. 787-816.
Chun, C. 1876. Ueber den Bau, die Entwickelung und physiologische Bedeutung der
Rektaldriisen bei den Insekten. Abh. Senckenb. naturf. Gesell., bd. 10, pp. 27-55.
4 taf. Separate, 1875, 31 pp., 4 taf. Frankfurt a. M.
Scudder, S. H. 1877. Antigeny or Sexual Dimorphism in Butterflies. Proc. Amer. Acad.
Arts Sc, vol. 12, pp. 150-158.
Forel, A. 1878. Der Giftapparat und die Analdriisen der Ameisen. Zeits. wiss Zool.,
bd. 30, supp., pp. 28-68, taf. 3, 4.
Schneider, R. 1878. Die Schuppen aus den verschiedenen Fliigel- und Korperteilen der
Lepidopteren. Zeits. gesammt. Naturw., bd. 51, pp. 1-59.
Scudder, S. H. 1881. Butterflies; Their Structure, Changes and Life-Histories, with
Special Reference to American Forms. 9+322 pp., 201 figs. New York. Henry
Holt & Co.
Klemensiewicz, S. 1882. Zur naheren Kenntniss der Hautdriisen bei den Raupen und
bei Malachius. Verb, zool.-bot. Gesell. Wien, bd. 32, pp. 459-474, 2 taf.
Dimmock, G. 1883. The Scales of Coleoptera. Psyche, vol. 4, pp. i-ii, 23-27, 43-47,
63-71, figs. i-ii.
Osten-Sacken, C. R. 1884. An Essay on Comparative Chaetotaxy, or the Arrangement
of Characteristic Bristles of Diptera. Trans. Ent. Soc. London, pp. 497-517.
Simmermacher, G. 1884. Untersuchungen iiber Haftapparate an Tarsalgliedern von
Insekten. Zeits. wiss. Zool., bd. 40, pp. 481-556, taf. 25-27, 2 figs.
Dahl, F. 1885. Die Fussdriisen der Insekten. Archiv mikr. Anat., bd. 25, pp. 236-263,
taf. 12, 13. —
Witlaczil, E. 1885. Die Anatomic der Psylliden. Zeits. wiss. Zool., bd. 42, pp. 569-638,
taf. 20-22.
Goossens, T. 1886. Des chenilles vesicantes. Ann. Soc. ent. France, ser. 6, t. 6, pp.
461-464.*
Minot, C. S. 1886. Zur Kenntniss der Insektenhaut. Archiv mikr. Anat., bd. 28, pp.
37-48, taf. 7.
LITERATURE 44 1
Schaffer, C. 1889. Beitrage zur Histologic der Insekten. Zool. Jahrb., Abth. Anat.
Ont., bd. 3, pp. 611-652, taf. 29, 30.
Packard, A. S. 1890. Notes on some points in the external structure and phylogeny of
lepidopterous larvje. Proc. Bost. Soc. Nat. Hist., vol. 25, pp. 82-114, pis. i, 2.
Borgert, H. 1891. Die Hautdriisen der Tracheaten. 81 pp., taf. Jena.
Kellogg, V. L. 1894. The Taxonomic Value of the Scales of the Lepidoptera. Kansas
Univ. Quart., vol. 3, pp. 45-89, pis. 9, 10, figs. 1-17.
Lutz, K. G. 1895. Das Bluten der Coccinelliden. Zool. Anz., jhg. 18, pp. 244-255, i fig.
Packard, A. S. 1895-96. The Eversible Repugnatorial Scent Glands of Insects. Journ.
N. Y. Ent. Soc, vol. 3, pp. 1 10-127, pl- 5; vol. 4, pp. 26-32.*
Spiiler, A. 1895. Beitrag zur Kenntniss des feineren Baues und der Phylogenie der
Fliigelbedeckung der Schmetterlinge. Zool. Jahrb., Abth. .\nat. Ont., bd. 8, pp.
520-543, taf. 36.
Mayer, A. G. 1896. The Development of the Wing Scales and their Pigment in Butterflies
and Moths. Bull. Mus. Comp. Zool., vol. 29, pp. 209-236, pis. 1-7.*
Bordas, L. 1897. Description anatomique et etude histologique des glandes a venin des
Insectes hymenopteres. 53 pp., 2 pis. Paris.
Cuenot, L. 1897. Sur la saignee reflexe et les moyens de defense de quelques Insectes.
Arch. Zool. e.xp., ser. 3, t. 4, pp. 655-680, 4 figs.
Hilton, W. A. 1902. The Body Sense Hairs of Lepidopterous Larva;. Amer. Nat., vol.
36, pp. 561-578, figs. 1-23.*
Tower, W. L. 1902. Observations on the Structure of the Exuvial Glands and the For-
mation of the Exuvial Fluid in Insects. Zool. Anz., bd. 25, pp. 466-472, figs. 1-8.
Tower, W. L. 1903. The Development of the Colors and Color Patterns of Coleoptera,
with Observations upon the Development of Color in Other Orders of Insects.
Univ. Chicago, Decenn. Publ., vol. 10, 140 pp., 3 pis.
Plotnikow, W. 1904. Uber die Hautung und iiber einige Elemente der Haut bei den
Insekten. Zeits. wiss. Zool., bd. 76, pp. 333-366, taf. 21, 22, 2 figs.
Kapzov, S. 1911. Untersuchungen iiber den feineren Bau der Cuticula bei Insekten.
Zeits. wiss. Zool., bd. 98, pp. 297-337, taf. 14-16, 3 figs.*
Deegener, P. 1912. Haut und Hautorgane In Schroder: Handbuch der Entomologie,
bd. I, pp. 1-60, figs. 1-38.*
MUSCULAR SYSTEM
Lyonet, P. 1762. Traite anatomique de la Chenille qui ronge le Bois de Saule. Ed. 2.
22 4- 616 pp., 18 pis. La Haye.
Straus-Durckheim, H. 1828. Considerations generales sur I'anatomie comparee Hes
animaux articules, etc. 434 pp., 10 pis. Paris.
Newport. G. 1839. Insecta. Todd's Cyclopaedia Anat. Phys., vol. 2, pp. 853-994, fig<;.
329-439.
Lubbock, J. 1859. On the Arrangement of the Cutaneous Muscles of the Larva of Py-
g^era bucephala. Trans. Linn. Soc. Zool., vol. 22, pp. 163-191, 2 pis.
Plateau, F. 1865, 1866. Sur la force musculaire des insectes. Bull. Acad. roy. Belgique,
ser. 2, t. 20, pp. 732-757; t. 22, pp. 283-308.
Lubbock, J. 1877. On some Points in the Anatomy of Ants. Month. Micr. Journ., vol.
18, pp. 121-142, pis. 189-192.
Lubbock, J. 1879. On the Anatomy of Ants. Trans. Linn. Soc. Zool., ser. 2, vol. 2, pp.
141-154, 2 pis.
Von Lendenfeld, R. 1881. Der Flug der Libellen. Ein Beitrag zur .\natomie und Phy-
siologic der Flugorgane der Insecten. Sitzb. Akad. Wiss. Wien, bd. 83, pp. 289-
376, taf. 1-7.
442 ENTOMOLOGY
Luks, C. 1882. Ueber die Brustmuskulatur der Insekten. Jenais. Zeits. Naturw., bd.
i6, pp. 529-552, taf. 22, 23.
Dahl, F. 1884. Beitrage zur Kenntnis des Baues und der Funktionen der Insektenbeine.
Archiv Naturg., jhg. 50, bd. i, pp. 146-193, taf. 11-13.
Van Gehuchten, A. 1886. Etude sur la structure intime de la cellule musculaire striee.
La Cellule, t. 2, pp. 289-453, pis. 1-6.
Miall, L. C, and Denny, A. 1886. The Structure and Life-history of the Cockroach.
London and Leeds.* (See pp. 71-84.)
Kolliker, A. 1888. Zur Kenntnis der quergestreiften Muskelfasern. Zeits. wiss. Zool.,
bd. 47, pp. 689-710, taf. 44, 45.
Biitschli, O., und Schewiakoff, W. 1891. Ueber den feineren Bau der quergestreiften
Muskeln von Arthropoden. Biol. Centralb., bd. 11, pp. 33-39, figs. 1-7.
Rollet, A. 1891. Ueber die Streifen N. (Nebenscheiben), das Sarkoplasma und
Contraktion der quergestreiften Muskelfasern. Archiv mikr. x\nat., bd. 37, pp.
654-684, taf. 37.
Janet, C. 1895. Etudes sur les Fourmis, les Guepes et les Abeilles. Note 12. Structure
des Membranes articulaires des Tendons et des Muscles (Myrmica, Camponotus,
Vespa, Apis). 26 pp., 11 figs. Limoges.
Janet, C. 1895. Sur les Muscles des Fourmis, des Guepes et des Abeilles. Compt. rend.
Acad. Sc, t. 121, pp. 610-613, I fig.
Bauer, A. 1910. Die Muskulatur von Dytiscus marginalis. Zeits. wiss. Zool., bd. 95,
pp. 594-646, figs. 1-19.*
Deegener, P. 1913. Muskulatur und Endoskelett. In Schroder: Handbuch der
Entomologie, bd. i, pp. 438-465, figs. 320-335.*
Kielich, J. 1918. Beitrage zur Kenntnis der Insectenmuskeln. Zool. Jahrb., Abth.
Anat. Ont., bd. 40, pp. 515-536, pis. 25-26.
NERVOUS SYSTEM
Newport, G. 1832, 1834. On the Nervous System of the Sphinx Ligustri Linn, and on the
changes which it undergoes during a part of the Metamorphoses of the Insect.
Phil. Trans. Roy. Soc. London, vol. 122, pp. 383-398, 2 pis.* Part II Phil.
Trans. Roy. Soc. London, vol. 124, pp. 389-423, 5 pis.
Leydig, F. 1857. Lehrbuch der Histologie des Menschen und der Thiere. 12 -1- 551 pp.,
figs. Frankfurt.
Flogel, J. H. L. 1878. Ueber den einheitlichen Bau des Gehirns in den verschiedenen
Insecten-Ordnungen. Zeits. wiss. Zool., bd. 30, Suppl., pp. 556-592, taf. 23, 24.
Newton, E. T. 1879. On the Brain of the Cockroach, Blatta orientalis. Quart. Journ.
Micr. Soc, n. s., vol. 19, pp. 340-356, pis. 15, 16.
Michels, H. 1880. Beschreibung des Nervensystems von Oryctes nasicornis imL^rven-,
Puppen- und Kaferzustande. Zeits. wiss. Zool., bd. 34, pp. 641-702, taf. 33-36.
Packard, A. S. 1880. The Brain of the Locust. Second Kept. U. S. Ent. Comm., pp.
223-242, pis. 9-15, fig. 9. Washington.*
Koestler, M. 1883. Ueber das Eingeweidenervensystem von Periplaneta orientalis.
Zeits. wiss. Zool., bd. 39, pp. 572-595, taf. 34.
Viallanes, H. 1884-87. Etudes histologiques et organologiques sur les centres nerveux et
les organes des sens des animaux articules. Mem. 1-5. Ann. Sc. nat. Zool.,
ser. 6, t. 17-19; ser. 7, t. 2, 4; 22 pis.
Leydig, F. 1885. Zelle und Gewebe. Neue Beitrage zur Histologie des Tierkorpers,
219 pp., 6 taf. Bonn.
Binet, A. 1894. Contribution a I'etude du system nerveux sous-intestinal des insectes.
Journ. Anat. Phys., t. 30, pp. 449-580, pis. 12-15, 23 figs.
LITERATURE 443
Pawlovi, M. I. 1895. On the Structure of the Blood- Vessels and Sympathetic Nervous
System of Insects, particularly Orthoptera. Works Lab. Zool. Cab. Imp. Univ.
Warsaw, pp. 96 + 22, tab. 1-6. In Russian.
Holmgren, E. 1896. Zur Kenntnis des Hauptnervensystems der Arthropoden. Anat.
Anz., bd. 12, pp. 449-457, 7 figs-
Kenyon, F. C. 1896. The Brain of the Bee. Journ. Comp. Neurol., vol. 6, pp. 133-210,
pis. 14-22.
Kenyon, F. C. 1896. The meaning and structure of the so-called "mushroom bodies"
of the hexapod brain. Amer. Nat., vol. 30, pp. 643-650, i fig.
Keynon, F. C. 1897. The optic lobes of the bee's brain in the light of recent neurological
methods. Amer. Nat., vol. 31, pp. 369-376, pi. 9-
Deegener, P. 1912. Nervensystem. In Schroder: Handbuch der Entomologie, bd. i,
pp. 76-139, figs- 39-78.*
Thompson, C. B. 1913. A Comparative Study of the Brains of Three Genera of Ants,
with Special Reference to the Mushroom Bodies. Journ. Comp. Zool., vol. 23,
PP- 515-572, 40 figs-*
SENSE ORGANS; SOUNDS
Miiller, J. 1826. Zur vergleichenden Physiologic des Gesichtsinnes der Menschen und
der Tiere. 462 pp., 8 taf. Leipzig.
Scudder, S. H. 1868. The Songs of the Grasshoppers. Amer. Nat., vol. 2, pp. 113-120..
5 figs-
Scudder, S. H. 1868. Notes on the Stridulation of Grasshoppers. Proc. Bost. Soc.
Nat. Hist., vol. 11, pp. 306-313.
Graber, V. 1872. Bemerkungen iiber die Gehor- und Stimmorgane der Heuschreckeh und
Cicaden. Sitzb. Akad. Wiss. Wien, math.-naturw. CI., bd. 66, pp. 205-213, 2 figs.
Paasch, A. 1873. Von den Sinnesorganen der Insekten im AUgemeinen von Gehor- und
Geruchsorganen im Besondern. Archiv Naturg., jhg. 39, bd. i, pp. 248-275.
Forel, A. 1874. Les fourmis de la Suisse. Neue Denks. allg. Schweiz. Gesell. Naturw.,
bd. 26, 480 pp., 2 taf. Separate, 1874, 4 + 457 pp., 2 taf. Geneve.
Mayer, A. M. 1874. Experiments on the supposed Auditory Apparatus of the Mosquito.
Amer. Nat., vol. 8, pp. 577-592, fig. 92.
Graber, V. 1876. Die tympanalen Sinnesapparate der Orthopteren. Denks. Akad.
Wiss. Wien, bd. 36, pp. 1-140, 10 taf.
Graber, V. 1876. Die abdominalen Tympanalorgane der Cicaden und Gryllodeen.
Denks. Akad. Wiss. Wien, bd. 36, pp. 273-296, 2 taf.
Mayer, P. 1877. Der Tonapparat der Cikaden. Zeits. wiss. Zool., bd. 28, pp. 79-92,
3 figs.
Lowne, B. T. 1878. On the Modifications of the Simple and Compound Eyes of Insects.
Phil. Trans. Roy. Soc. London, vol. 169, pp. 577-602, pis. 52-54.
Grenacher, H. 1879. Untersuchungen iiber das Sehorgan der Arthropoden, insbesondere
der Spinnen, Insekten und Crustaceen. 8 + 188 pp., 11 taf. Gottingen.
Hauser, G. 1880. Physiologische und histiologische Untersuchungen uber das Geruchs-
organ der Insekten. Zeits. wiss. Zool., bd. 34, pp. 367-403, taf. 17-19.
Graber, V. 1882. Die chordotonalen Sinnesorgane und das Gehor der Insecten. Archiv
mikr. Anat., bd. 20, pp. 506-640, taf. 30-35, 6 figs.; bd. 21, pp. 65-145, 4 figs.*
Lubbock, J. 1882. Ants, Bees and Wasps. 19 + 448 pp-, 5 pls-, 31 figs- London.
1884, 1901, New York. D. Appleton & Co.
Graber, V. 1883. Fundamentalversuche iiber die Helligkeits- und Farbenempfindlichkeit
augenloser und geblendeter Tiere. Sitzb. Akad. Wiss. Wien, bd. 87, pp. 201-236.
Graber, V. 1884. GrundUnien zur Erforschung des Helligkeits und Farbensinnes der
Tiere. 8-1-322 pp. Prag und Leipzig.
444 ENTOMOLOGY
Lee, A. B. 1884. Bemerkungen iiber den feineren Bau der Chordotonal-Organe. Archiv
mikr. Anat., bd. 23, pp. 133-140, taf. 7b.
Lowne, B. T. 1884. On the Compound Vision and the Morphology of the Eye in Insects.
Trans. Linn. Soc. Zool., vol. 2, pp. 389-420, pis. 40-43.
Carriere, J. 1885. Die Sehorgane der Thiere, vergleichend anatomischdargestellt. 6 +
205 pp., I taf., 147 figs. Miinchen und Leipzig. R. Oldenbourg.
Hickson, S. J. 1885. The Eye and Optic Tract of Insects. Quart. Journ. Micr. Sc, vol.
25, pp. 215-251, pis. 15-17.
Plateau, F. 1885-88. Recherches experimentales sur la vision chez les Insectes. Bull.
Acad. roy. Belgique, ser, 3, t. 10, 14, 15, 16. Mem. Acad, roy. Belgique, t. 43, pp.
1-9 1.
Will, F. 1885. Das Geschmacksorganderlnsekten. Zeits. wiss. Zool., bd. 42., pp. 674-
707, taf. 27.
Forel, A. 1886-87. Experiences et remarques critiques sur les sensations des Insectes.
Rec. zool. Suisse, t. 4, pp. 1-50, 145-240, pi. i.
Mark, E. L. 1887. Simple Eyes in Arthropods. Bull. Mus. Comp. Zool., vol. 13, pp. 49-
105, pis. 1-5.
Patten, W. 1887, 1888. Studies on the Eyes of Arthropods. I. Development of the
Eyes of Vespa, with Observations on the Ocelli of some Insects. Journ. Morph.,
vol. I, pp. 193-226, I pi. II. Eyes of Acilius. Journ. Morph., vol. 2^ pp. 97-190,
pis. 7-13.
Lubbock, J. 1888, 1902. On the Senses, Instincts and Intelligence of Animals, with
Special Reference to Insects. 29 + 292 pp., 118 figs. New York. D. Appleton
&Co.
Vom Rath, O. 1888. Ueber die Hautsinnesorgane der Insekten. Zeits. wiss. Zool., bd.
46, pp. 413-454, taf. 30, 31.
Ruland, F. 1888. Beitrage zur Kenntnis der antennalen Sinnesorgane der Insekten.
Zeits. wiss. Zool., bd. 46, pp. 602-628, taf. 37.
Lowne, B. T. 1889. On the Structure of the Retina of the Blowfly (Calliphora erythro-
cephala). Journ. Linn. Soc. Zool., vol. 20, pp. 406-417, pi. 27.
Packard, A. S. 1889. Notes on the Epipharynx, and the Epipharyngeal Organs of Taste
in Mandibulate Insects. Psyche, vol. 5, pp. 193-199, 222-228.
Pankrath, O. 1890. Das Auge der Raupen und Phryganidenlarven. Zeits. wiss. Zool.,
bd. 49, PP- 690-708, taf. 34, 35.
Stefanowska, M. 1890. La disposition histologique du pigment dans les yeux des Arthro-
podes sous I'influence de la lumiere directe et de I'obscurite complete. Rec. zool.
Suisse, t. 5, pp. 151-200, pis. 8, 9.
Watase, S. 1890. On the Morphology of the Compound Eyes of Arthropods. Studies
Biol. Lab. Johns Hopk. Univ., vol. 4, pp. 287-334, pis. 29-35.
Weinland, E. 1890. Ueber die Schwinger (Halteren) der Dipteren. Zeits. wiss. Zool.,
bd. 51, pp. 55-166, taf. 7-11.
Exner, S. 1891. Die Physiologic der fazettierten Augen von Krebsen und Insekten.
8 + 206 pp., 8 taf., 23 figs. Leipzig und Wien.
Von Adelung, N. 1892. Beitrage zur Kenntnis des tibialen Gehorapparates der Locusti-
den. Zeits. wiss. Zool., bd. 54, pp. 316-349, taf. 14, 15.
Nagel, W. 1892. Die niederen Sinne der Insekten. 68 pp., 19 figs. Tubingen.
Child, C. M. 1894. Ein bisher wenig beachtetes antennales Sinnesorgan der Insekten,
mit besonderer Beriicksichtigung der Culiciden und Chironomiden. Zeits. wiss.
Zool, bd. 58, pp. 475-528, taf. 30, 31.
Mallock, A. 1894. Insect Sight and the Defining Power of Composite Eyes. Proc. Roy.
Soc. London, vol. 55, pp. 85-90, figs. 1-3.
LITERATURE 445
Vom Rath, O. 1896. Zur Kenntnis der Hautsinnesorgane und des scnsiblen Nerven-
systems der Arthropoden. Zeits. wiss. Zool., bd. 61, pp. 499-539, taf. 23, 24.
Redikorzew, W. 1900. Untersuchungen uber den Bau der Ocellen der Insekten. Zeits.
wiss. Zool., bd. 68, pp. 581-624, taf. 39, 40, figs. 1-7.
Reuter, E. 1896. Ueber die Palpen der Rhopaloceren, etc. Acta See. Sc. Fenn., t. 22,
pp. 16 4- 578, 6 tab.
Hesse, R. 1901. Untersuchungen uber die Organe der Lichtempfindung bei niederen
Thieren. VII. Von den Arthropoden- Augen. Zeits. wiss. Zool., bd. 70, pp. 347-
473, taf. 16-21, figs. I, 2.
Schenk, O. 1903. Die antennalen Hautsinnesorgane einiger Lepidoptcren und Hymen-
opteren mit besonderer Beriicksichtigung der sexuellen Unterschiede. Zool.
Jahrb., Abth. Anat. Ont., bd. 17, pp. 573-618, taf. 21, 22, 4 figs.*
Shull.A.F. 1907. TheStridulationof the Snowy Tree-cricket ((Ecanthusniveus). Can.
Ent., vol. 39, pp. 213-225, figs. 14, 15.*
Forel, A. 1908. The Senses of Insects. Trans, by M. Yearsley. 14 + 324 pp., 2 pis.
London. Methucn & Co.*
Dietrich, W. 1909. Die Facettenaugen der Dipteren. Zeits. wiss. Zool., bd. 92, pp.
465-539, taf. 22-25, 17 figs.*
Link, £. 1909. Ueber die Stirnaugen der Neuropteren und Lepidopteren. Zool. Jahrb.,
Abt. Anat. Ont., bd. 27, pp. 213-242, taf. 15-17, 5 figs.*
Link, E. 1909. Ueber die Stirnaugen der hemimetabolen Insecten. Zool. Jahrb., Abt.
Anat. Ont , bd. 27, pp. 281-376, taf. 21-24, i4 figs.*
Lovell, J. H. 1910, 1912. The Color Sense of the Honey Bee. Amer. Nat., vol. 44, pp.
673-692; vol. 46, pp. 83-107.
Turner, C. H. 1910. Experiments on Color-vision of the Honey-bee. Biol. Bull., vol. 19,
pp. 257-279, 3 figs.
Allard, H. A. 1911. Studying the Stridulations of Orthoptera. Proc. Ent. Soc. Wash.,
vol. 13, pp. 141-148.
Schon, A. 1911. Bau und Entwicklung des tibialen Chordotonalorgans bei der Honigbiene
und bei Ameisen. Zool. Jahrb., Abt. Anat. Ont., bd. 31, pp. 439-472, taf. 17-19,
9 figs.*
DemoU, R., and Scheuring, L. 1912. Die Bedeutung der Ocellen der Insecten. Zool.
Jahrb., Abt. Allg. Zool. Phys., bd. 31, pp. 519-628, 23 figs.*
Giinther, K. 1912. Die Sehorgane der Larve und Imago von Dytiscus marginalis. Zeits.
wiss. Zool., bd. 100, pp. 60-115, 36 figs.*
Hochreuther, P. 1912. Die Hautsinnesorgane von Dytiscus-margina'.is L., ihr Bau und
ihre Verbreitung am Korper. Zeits. wiss. Zool., bd. 103, pp. 1-114, 102 figs.*
Prochnow, O. 1912. Die Organe zur Lautausserung. In Schroder: Handbuch der
Entomologie., bd. i, pp. 61-75, figs. 1-12.*
Deegener, O. 1912-13. Sinnesorgane. In Schroder: Handbuch der Entomologie, bd.
I, pp. 140-233, figs- 79-152.*
Caesar, C. J. 1913. Die Stirnaugen der Ameisen. Zool. Jahrb., Abt. Anat. Ont., bd.
35, pp. 161-240, taf. 7-10, 29 figs.*
Jorschke, H. 1914, Die Facettenaugen der Orthopteren und Termiten. Zeits. wiss.
Zool., bd. Ill, pp. 153-280, figs. 1-57, pi. 4*
Mclndoo, N. E. 1914. The Olfactory Sense of the Honey Bee. Journ. Exp. Zool., vol.
16, pp. 265-346, 24 figs.*
Mclndoo, N. E. 1914. The Olfactory Sense of Hymenoptera. Proc. Acad. Nat. Sc,
pp. 294-341, 3 figs., pis. II, 12.*
Mclndoo, N. E. 1914. The Scent-producing Organ of the Honey Bee. Proc. Acad.
Nat. Sc, pp. 542-555, I fig., pis. 19, 20.*
446 ENTOMOLOGY
Mclndoo, N. E. 1914. The Olfactory Sense of Insects. Smithson. Misc. Coll., vol. 63,
no. 9, pp. 1-63, figs. 1-6.*
Mclndoo, N. E. 1915. The Olfactory Sense of Coleoptera. Biol. Bull., vol. 28, pp.
407-460, 2 pis.*
Mclndoo, N. E. 1916. The Sense Organs on the Mouth Parts of the Honey Bee. Smith-
son. Misc. Coll., vol. 65, no. 14, 55 pp., 10 figs.*
Demoll, R. 1917. Die Sinnesorgane der Arthropoden, ihr Ban und ihre Funktion. 243
pp. Braunschweig.
Mclndoo, N. E. 1917. The Olfactory Organs of Lepidoptera. Journ. Morph., vol. 29,
PP- 33-54, 10 figs.*
Mclndoo, N. E. 1918. The Olfactory Organs of a Coleopterous Larva. Journ. Morph.,
vol. 31, pp. 1 13-13 1, 33 figs-*
Mclndoo, N. E. 1918. The Olfactory Organs of Diptera. Journ. Comp. Neur., vol. 29,
pp. 457-484, 55 figs.*
Mclndoo, N. E. 1919. The Olfactory Sense of Lepidopterous Larvae. Ann. Ent. Soc.
Amer., vol. 12, pp. 65-84, figs. 1-53-*
Eltrihgham, H. 1919. . Butterfly Vision. Trans. Ent. Soc. London, pp. 1-49, pis. 1-5.
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31, pp. 405-427, 92 figs.*
DIGESTIVE SYSTEM
Fabre, J. L. 1862. Etude sur le r6le du tissu adipeux dans la secretion urinaire chez les
Insectes. Ann. Sc. nat. Zool., ser. 4, t. 19, pp. 351-382.
Plateau, F. 1874, Recherches sur les phenomenes de la digestion chez les Insectes. Mem.
Acad, ro}^ Belgique, t. 41, 124 pp., 3 pis.
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Helm, F. E. 1876. Ueber die Spinndriisen der Lepidopteren. Zeits. wiss. Zool., bd. 26,
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Plateau, F. 1877. Note additionelle au Memoire sur les phenomenes de la digestion chez
les Insectes. Bull. Acad. roy. Belgique, ser. 2, t. 44, pp. 710-733.
Wilde, K. F. 1877. Untersuchungen iiber den Kaumagen der Orthopteren. Archiv
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De Bellesme, J. 1878. Travaux originaux de Physiologie comparee. I. Insectes.
Digestion, Metamorphoses. 252 pp., 5 pis. Paris.
Schindler, E. 1878. Beitrage zur Kenntniss der Malpighi'schen Gefasse der Insecten
Zeits. wiss. Zool., bd. 30, pp. 587-660, taf. 38-40.
Frenzel, J. 1882. Ueber Bau und Thatigkeit des Verdauungskanals derLarve des Tene-
brio moUtor mit Beriicksichtigung anderer Arthropoden. Berl. ent Zeits., bd.
26, pp. 267-316, taf. 5.*
Leydig, F. 1883. Untersuchungen zur Anatomic und Histologic der Thiere. 174 pp.,
8 taf. Bonn.
MetschnikoflF, E. 1883. Untersuchungen iiber die intrazeUulare Verdauung bei wirbel-
losen Tieren. Arb. .zool. Inst. Wien, bd. 5, pp. 141-168, 2 taf.
Schiemenz, P. 1883. Ueber das Herkommen des Futtersaftes und die Speicheldriisen
der Biene nebst cinen Anhangc iiber das Reichorgan. Zeits. wiss. Zool., bd. 38,
pp. 71-135, taf. 5-7.
Locy, W. A. 1884. Anatomy and Physiology of the family Nepidae. Amer. Nat., vol. 18,
pp. 250-255, 353-367, pis. 9-12.
LITERATURE 447
Witlaczil, E. 1885. Zur ISlorphologie unci Anatomie der Cocciden. Zeits. wiss. Zool.,
bd. 43, PP- 149-174, taf. 5.
Frenzel, J. 1886. Einigesiiber den Mitteldarm derlnsekten, so\\ae iiber Epithelregenera-
tion. Archiv mikr. Anat., bd. 26, pp. 229-306, taf. 7-9.
Kniippel, A. 1886. Ueber Speicheldriisen von Insecten. Archiv Naturg., jhg. 52, bd. i,
pp. 269-303, taf. 13, 14.
Cholodkovsky, N. 1887. Sur la morphologic de I'appareil urinaire des Lepidopteres.
Archiv. Biol., t. 6, pp. 497-514, pi. 17.
Faussek, V. 1887. Beitrage zur Histologic dcs Darmkanals dcr Insekten. Zcits. wiss.
Zool., bd, 45, pp. 694-712, taf. 36.
Blanc, L. 1889. Etude sur la secretion de la soie et sur la structure du brin ct de la have
dans Ic Bombyx mori. 56 pp., 4 pis. Lyon.
Kowalevsky, A. 1889. Ein Beitrag zur Kenntnis dcr Exkretionsorgane. Biol. Ccntralb.,
bd. 9, pp. 33-47- 65-76, 127-128.
Van Gehuchten, A. 1890. Recherches histologiques sur I'appareil digestif de la larve de
la Ptychoptera contaminata, I Part. Etude du revetement epithelial et recher-
ches sur la secretion. La Cellule, t. 6, pp. 183-291, pis. 1-6.
Gilson, G. 1890, 1893. Recherches sur les cellules secretantcs. La soie et les appareils
sericigenes. I. Lepidopteres; II. Trichopteres, La Cellule, t. 6, pp. 115-182, pis.
1-3; t. 10, pp. 37-63, pl- 4-
Blanc, L. 1891. La tete du Bomby.x mori a I'etat larvaire, anatomie et physiologic.
Trav. Lab. Etud. Soie, 1889-1890, 180 pp., 95 figs. Lyon.
Wheeler, W. M. 1893. The primitive number of Malpighian vessels in Insects. Psyche,
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Bordas, L. 1895. Appareil glandulairc des Hymenopteres. (Glandcs salivaires, tube
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Bordas, L. 1897. L'appareil digestif dcs Orthopteres. Ann. Sc. nat. Zool., ser. 8, t. 5, pp.
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Folsom, J. W., and Welles, M. U. 1906. Epithelial Degeneration, Regeneration, and
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Deegener, P. 1913. Der Darmtraktus und seine Anhange. In Schroder: Handbuch der
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CIRCULATORY SYSTEM
Graber, V. 1873. Ueber den propulsatorischen Apparat der Insekten. Archiv mikr.
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Graber, V. 1873. Ueber die Blutkorperchen der Insekten. Sitzb. Akad. Wiss. Wien,
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Graber, V. 1876. Ueber den pulsierendenBauchsinus dcr Insekten. Archiv mikr. Anat.,
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Dogiel, J. 1877. Anatomie und Physiologic des Herzens der Larve von Corethra plumi-
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448 ENTOMOLOGY
Viallanes, H. 1882. Recherches sur I'histologie des Insectes, et sur les phenomenes histo-
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Dewitz, H. 1889. Eigenthatige Schwimmbewegung der Blutkorperchen der Glieder-
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FAT BODY
Gadeau de Kerville, H. 1881, 1887. Les insectes phosphorescents. T. i, 55 pp., 4 pls-'.
t. 2, 135 pp. Rouen.*
Von Wielowiejski, H. R. 1882. Studien uber Lampyriden. Zeits. wiss. Zool., bd. 37;
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Von Wielowiejski, H. 1883. Ueber den Fettkorper von Corethra plumicornis und seine
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Emery, C. 1884. Untersuchungen liber Luciola italica L. Zeits. wiss. Zool., bd. 40, PP-
338-355, taf. 19.
Dubois, R. 1886. Contribution a I'etude de la production de la lumiere par les etres
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Heinemann C. 1886. Zur .\natomie und Physiologic der Leuchtorgane mexikanischer
Cucuj'o's. Archiv mikr. Anat., bd. 27, pp. 296-382.
Von Wielowiejski, H. R. 1886. Ueber das Blutgewebe der Insekten. Zeits. wiss. Zool.,
bd. 43, PP- 512-536. , ^, ,-,j ^ J
Schaflfer, C. 1889. Beitrage zur Histologie der Insekten. III. Ueber Blutbildungsherde
bei Insektenlarven. Zool. Jahrb., Abth. Anat. Ont., bd. 3, pp. 626-636, taf. 30.
Von Wielowiejski, H. R. 1889. Beitrage zur Kenntnis der Leuchtorgane der Insecten.
Zool. Anz., jhg. 12, pp. 594-600.
Wheeler, W. M, 1892. Concerning the "blood tissue" of the Insecta. Psyche, vol. 6,
pp. 216-220, 233-236, 253-258, pi. 7.
Cuenot, L. 1895. Etudes physiologiques sur les Orthopteres. Arch. Biol., t. 14, pp.
293-341, pls. 12, i^.
Schmidt, P. 1895. On the Luminosity of Midges (Chironomidae). x\nn. Mag. Nat. Hist.,
ser. 6, vol. 15, pp. 133-141- Trans, from Zool. Jahrb., Abth. Syst., etc., bd. 8, pp.
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Bruntz, L. 1904. Contribution a I'Etude de I'excretion chez les Arthropodes. Archiv.
Biol., t. 20, pp. 217-420, pls. 7-9.
Townsend, A. B. 1904. The Histology of the Light Organs of Photinus margineUus.
Amer. Nat., vol. 38, pp. 127-151, figs, i-ii.*
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LITERATURE 449
McDermott, F. A. 1911. Some Further Observations on the Light Emission of American
Lampyrida". Can. Knt., vol. 43, pp. 399-406.
Coblentz, W. W. 1912. A Physical Study of the Firefly. Publ. No. 164, Carnegie Inst.,
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Glaser, R. W. 1912. A Contribution to Our Knowledge of the Function of the (Enocytes
of Insects. Biol. Bull., vol. 23, pp. 213-224.*
McDermott, F. A. 1912. Recent Advances in Our Knowledge of the Production of Light
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RESPIRATORY SYSTEM
Dufour, L. 1852. Ktudes anatomiques et physiologiques et observations sur les larves des
Libellules. Ann. Sc. nat. Zool., ser. 3, t. 17, pp. 65-110, 3 pis.
Williams, T. 1853-57. On the Mechanism of Aquatic Respiration and on the Structure
of the Organs of Breathing in Invertebrate Animals. Trans. Ann. Mag. Nat.
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Rathke, H. 1861. Anatomisch-physiologische Untersuchungen uber den Athmungspro-
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Landois, H., und Thelen, W. 1867. Der Tracheenverschluss bei den Insekten. Zeits.
wiss. Zool., bd. 17, pp. 187-214, I taf.
Gerstacker, A. 1874. Ueber das Vorkommen von Tracheenkiemen bei ausgebildeten
Insecten. Zeits. wiss. Zool., bd. 24, pp. 204-252, i taf.
Packard, A. S. 1874. On the Distribution and Primitive Number of Spiracles in Insects.
Amer. Nat., vol. 8, pp. 531-534-
Palmen, J. A. 1877. Zur Morphologic des Tracheensystems. 10 + i49 PP-. 2 taf.
Helsingfors.
Sharp, D. 1877. Observations on the Respiratory Action of the Carnivorous Water
Beetles (Dytiscidae). Journ. Linn. Soc. Zool., vol. 13, pp. 161-183.
Poletajew, O. 1880. Quelques mots sur les organes respiratoires des larves des Odonates.
Hora; Soc. Ent. Ross., t. 15, pp. 436-452, 2 pis.
Krancher, O. 1881. Der Bau der Stigmen bei den Insekten. Zeits. wiss. Zool., bd. 35,
PP- 505-574, taf. 28, 29.
Vayssiere, A. 1882. Recherches sur I'organisation des larves des Ephemerines. Ann. Sc.
nat. Zool., ser. 6, t. 13, pp. 1-137, pls. i-n.
Macloskie, G. 1884. The Structure of the Tracheae of Insects. Amer. Nat., vol. 18, pp.
567-573, figs. 1-4.
Plateau, F. 1884. Recherches experimentales sur les mouvements respiratoires des
Insectes. Mem. Acad. roy. Belgique, t. 45, 219 pp., 7 pis., 56 figs.
Raschke, E. W. 1887. Die Larve von Culex nemorosus. Archiv Naturg., jhg. 53, bd. i,
pp. 133-163, taf. 5, 6.
Schmidt-Schwedt, E. 1887. Ueber Athmung der Larven und Puppen von Donacia
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Haase, E. 1889. Die Abdominalanhange der Insekten mit Beriicksichtigung der Myri-
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Cajal, S. R. 1890. Coloration par la methode de Golgi des terminaisons des trachees et
des nerfs dans les muscles des ailes des insectes. Zeits. wiss. Mikr., bd. 7, pp. 332-
342, taf. 2, figs. 1-3.
Von Wistinghausen, C. 1890. Ueber Tracheenendigungen in den Sericterien der Raupen .
Zeits. wiss. Zool., bd. 49, pp. 565-582, taf. 27.*
Stokes, A. C. 1893. The Structure of Insect Tracheae, with Special Reference to those of
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29
450 ENTOMOLOGY
Miall, L. C. 1895, 1903. The Natural History of Aquatic Insects, ii + 39S pp., 116
figs. London and New York. Macmillan & Co.
Sadones, J. 1895. L'appareil digestif et respiratoire larvaire des Odonates. La Cellule,
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Gilson, G., and Sadones, J. 1896. The Larval Gills of the Odonata. Journ. Linn. Soc.
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Manunen, H. 1912. Ueber die Morphologie der Heteropteren und Homopterenstigmen.
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REPRODUCTIVE SYSTEM
Huxley, T. H. 1858-59. On the Agamic Reproduction and Morphology of Aphis
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Biitschli, O. 1871. Nahere Mittheilungen iiber die Entwicklung und den Bau der Samen-
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Palmen, J. A. 1884. Ueber paarige Ausfiihrungsgange der Geschlechtsorgane bei Insecten.
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Gilson, G. 1885. Etude comparee de la spermatogenese chez les Arthropodes. La
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Schneider, A. 1885. Die Entwicklung der Geschlechtsorgane der Insecten. Zool.
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La Valette St. George. 1886, 1887. Spermatologische Beitrage. Arch. mikr. Anat.,
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Von Wielowiejski, H. R. 1886. Zur Morphologie des Insectenovariums. Zool. Anz.,
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Zeits. wiss. Zool., bd. 45, pp. 327-397, taf. 18, 19.
Oudemans, J. T. 1888. Beitrage zur Kenntniss der Thysanura und Collembola. Bijdr.
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Leydig, F. 1889. Beitrage zur Kenntniss des thierischen Eies im unbefruchteten Zu-
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Ballowitz, E. 1890. Untersuchungen iiber die Struktur der Spermatozoen, zugleich ein
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Henking, H. 1890-92. Untersuchungen iiber die ersten EntwicklungsvorgSnge in der
Eiern der Insekten. Zeits. wiss. Zool., bd. 49, pp. 503-564, taf. 24-26; bd. 51, pp
685-736, taf. 35-37; bd. 54, pp. 1-274, taf. 1-12, figs. 1-12.
LITERATURE 45 1
Heymons, R. 1891. Die Entwicklung der weiblichen Geschlechtsorgane von Phyllo-
dromia (Blatta) germanica L. Zeits. wiss. Zool., bd. 53, pp. 434-536, taf. 18-20.
Ingenitzky, J. 1893. Zur Kenntnis der Begattungsorgane derLibelluliden. Zool. Anz.,
jhg. 16, pp. 405-407, 2 figs.
Escherich, K. 1894. Anatomische Studien uber das mannliche Genital-system der Cole-
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Toyama, K. 1894. On the Spermatogenesis of the Silk Worm. Bull. Coll. Agr. Univ.
Tokyo, vol. 2, pp. 125-157, pis. 3, 4.
Kluge, M.H. E. 1895. Das mannliche Geschlechtsorgan von Vespa germanica. Archiv.
Naturg., jhg. 61, bd. i, pp. 159-198, taf. 10.
Peytoureau, A. 1895. Contributions a I'etude de la morphologic de I'armure genitale des
Insectes. 248 pp., 22 pis., 43 figs. Paris.
Wilcox, E. V. 1895. Spermatogenesis of Caloptenus femur-rubrum and Cicada tibicen.
Bull. Mus. Comp. Zool., vol. 27, pp. 1-32, pis. 1-5.*
Wilcox, E. V. 1896. Futher Studies on the Spermatogenesis of Caloptenus femur-rubrum .
Bull. Mus. Comp. Zool., vol. 29, pp. 193-202, pis. 1-3.
Fenard, A. 1897. Recherches sur les organes complementaires internes de I'appareil
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Gross, J. 1903. Untersuchungeniiber die Histologic des Insectenovariums. Zool. Jahrb.,
Abth. Anat. Ont., bd. 18, pp. 71-186, taf. 6-14.*
Griinberg, K. 1903. Unte|rsuchungen liber die Keim- und Nahrzellen in den Hoden und
Ovarien der Lepidoptera. Zeits. wiss. Zool., bd. 74, pp. 327-39S> taf. 16-18.
Holmgren, N. 1903. Ueber vivipare Insecten. Zool. Jahrb., bd. 19, pp. 431-468,
10 figs.*
Felt, E. P. 1911. Miastor americana Felt, an Account of Pedogenesis. Twenty-sixth
Rept. St. Ent. N.Y., pp. 82-104, figs. 7-9.*
Deegener, P. 1913, 1921. Geschlechtsorgane. In Schroder: Handbuch der Entomo-
logie, bd. I, pp. 466-533, figs. 336-390-*
Doncaster, L. 1914. The Determination of Sex. 12 -}- 172 pp., 22 pis. Cambridge.,
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Doncaster, L. 1920. An Introduction to the Study of Cytology. 14 + 280 pp., figs.
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EMBRYOLOGY
Leuckart, R. 1858. Die Fortpflanzung und Entwicklung der Pupiparen nach Beobach-
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taf.
Weismann, A. 1863. Die Entwicklung der Dipteren im Ei, nach Beob'achtungen an
Chironomus spec, Musca vomitoria und Pulex canis. Zeits. wiss. Zool., bd. 13,
pp. 107-220, 7 taf. Separate, 1864, 263 pp., 14 taf.
Metschnikoff, E. 1866. Embryologische Studien an Insecten. Zeits. wiss. Zool., bd. 16,
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Brandt, A. 1869. Beitrage zur Entwicklungsgeschichtc der Libelluliden und Hemipteren.
Mem. Acad. St. Petersbourg, ser. 7, t. 13, pp. 1-33, 3 pis.
Melnikow,N. 1869. Beitrage zur Embryonalentwicklung der Insekten. Archiv Naturg.,
jhg. 35, bd. I, pp. 136-189, 4 taf.
Butschli, O. 1870. Zur Entwicklutagsgeschichte der Bienc. Zeits. wiss. Zool., bd. 20,
pp. 519-564, taf. 24-27.
Kowalevsky, A. 1871. Embryologische Studien an Wiirmern und Arthropoden. Mem.
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452 ENTOMOLOGY
Hatschek, B. 1877. Beitrage zur Entwicklungsgeschichte der Lepidopteren. Jenais.
Zeits. Naturw., bd. ii, 38 pp., 3 taf., 2 figs.
Bobretzky, N. 1878. Ueber die Bildung des Blastoderms und der Keimblatter bei den'
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Will, L. 1883. Zur Bildung des Eies und des Blastoderms bei den viviparen Aphiden.
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Ayers, H. 1884. On the Development of Qicanthus niveus and its Parasite Teleas.
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Patten, W. 1884. The Development of Phryganids, with a Preliminary Note on the
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Witlaczil, E. 1884. Entwicklungsgeschichte der Aphiden. Zeits. wiss. Zool., bd. 40, pp.
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Korotneflf, A. 1886. Die Embryologie der Gryllotalpa. Zeits. wisB. Zool, bd. 41, pp.
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Blochmann, F. 1887. Ueber die Richtungskorper bei Insecteneiern. Morph. Jahrb.,
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Biitschli, O. 1888. Bemerkungen iiber die Entwicklungsgeschichte von Musca. Morph.
Jahrb., bd. 14, pp. 170-174, 3 figs.
Graber, V. 1888. Ueber die Polypodie bei Insekten-Embryonen. Morph. Jahrb., bd.
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Henking, H. 1888. Die ersten Entwicklungsvorgange im Fliegenei und freie Kernbildung.
Zeits. wiss. Zool., bd. 46, pp. 289-336, taf. 23-26, 3 figs.
"Will, L. 1888. Entwicklungsgeschichte der viviparen Aphiden. Zool. Jahrb., Abth.
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Cholodkovsky, N. 1889. Studien zur Entwicklungsgeschichte der Insekten. Zeits.
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Graber, V. 1889. Ueber den Bau und die phylogenetische Bedeutung der embryonalen
Bauchanhange der Insekten. Biol. Centralb., jhg. 9, pp. 355-363.
Heider, K. 1889. Die Embryonalentwicklung von Hydrophilus piceus L. I. Theil. 99
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Wheeler, W. M. 1889. The Embryology of Blatta germanica and Doryphora decem-
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Carriere, J. 1890. Die Entwicklung der Mauerbiene (Chalicodoma muraria Fabr.) im
Ei. Archiv mikr. Anat., bd. 35, pp. 141-165, taf. 8, 8a.
Henking, H. 1890-92. Untersuchungen' iiber die ersten Entwicklungsvorgange in der
Eiern der Insekten. Zeits. wiss. Zool., bd. 49, pp. 503-564, taf. 24-26; bd. 51, pp.
685-736, taf. 35-37; bd. 54, pp. 1-274, taf. 1-12, figs. 1-12.
Wheeler, W. M. 1890. On the Appendages of the First Abdominal Segment of Embryo
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Cholodkowsky, N. 1891. Die Embryonalentwicklung, von Phyllodromia (Blatta ger-
manica). Mem. Acad. St. Petersbourg, ser. 7, t. 38, 4 + 120 pp., 6 pis., 6 figs.
Graber, V. 1891. Ueber die embryonale Anlage des Blut- und Fettgewebes der Insekten;
Biol. Centralb., jhg. 11, pp. 212-224.
Wheeler, W. M. 1891. Neuroblasts in the Arthropod Embryo. Journ. Morph., vol. 4,
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Graber, V. 1892. Ueber die morphologische Bedeutung der ventralen Abdominalan-
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Korschelt, E., iind Heider, K. 1892. Lehrbuch der vergleichenden Entwicklungsge-
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LITERATURE 453
M. Bernard and M. F. Woodward. Text-Book of the Embryology of Inverte-
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Wheeler, W. M. 1893. A Contribution to Insect Embryology. Journ. Morph., vol. 8,
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Heymons, R. 1895. Die Embryonalentwickelung von Ucrmapteren und Orthopter^n
unter besonderer Beriicksichtigung der Keimblatterbildung. 8 -|- 136 pp, 12 taf.,
33 figs. Jena.
He5rmons, R. 1896. Grundzuge der Entwickelung und des Korperbaues von Odonaten
und Ephemeriden. Anh. Abh. Akad. Wiss. Berlin, 66 pp., 2 taf.
Hesmions, R. 1897. Entwicklungsgeschichtliche Untersuchungen an Lepisma saccharina
L. Zeits. wiss. Zool., bd. 62, pp. 583-631, taf. 29, 30, 3 figs.
Kulagin, N. 1897. Beitriige zur Kenntnis der Entwicklungsgeschichte von Platygaster,
Zeits. wiss. Zool., bd. 63, pp. 195-235, taf. 10, 11.
Claypole, A. M. 1898. The Embryology and Oogenesis of Anurida maritima (Guer.),
Journ. Morph., vol. 14, pp. 219-300, pis. 20-25, 11 figs.
Uzel, H. 1898. Studien uber die Entwicklung der apterygoten Insecten. 6 + 58 pp
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Wilson, E. B. 1900. The Cell in Development and Inheritance. 21 + 483 pp., 194 figs
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Marchal, P. 1904. La Polyembryonie Specifique. Arch. Zool. exp. gen., ser. 4, t. 2, pp
257-335, pis. 9-I3-*
Heymons, R. 1912. Ueber den Genitalapparat und die Entwicklung von Hemimerus
talpoides Walk. Zool. Jahrb., Supplement 15, bd. 2, pp. 141-184, pis. 7-1 1, 3 figs
Korschelt, E. 1912. Zur Embryonalentwicklung des Dytiscus marginalis L. Zool
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Blunck, H. 1914. Die Entwicklung des Dytiscus marginalis L. vom Ei bis zur
Imago. I Teil. Zeits. wiss. Zool., bd. iii, pp. 76-151, figs. 1-31.*
Nelson, J. A. 1915. The Embryology of the Honey Bee. 4 + 282 pp., 95 figs., 6 pis.
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Strindberg, H. 1916. Zur Entwicklungsgeschichte und Anatomie der Mallophagen.
Zeits. wiss. Zool., bd. 115, pp. 382-459, figs. 1-38.*
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POSTEMBRYONIC DEVELOPMENT. METAMORPHOSIS
Weismann, A. 1864. Die nachembryonale Entwicklung der Musciden nach Beobach-
tungen an Musca vomitoria und Sarcophaga carnaria. Zeits. wiss. Zool., bd. 14,
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Weismann, A. 1866. Die Metamorphose von Corethra plumicornis. Zeits. wiss. Zool.,
bd. 16, pp. 45-127, 5 taf.
Trouvelot, L. 1867. The American Silk Worm. Amer. Nat., vol. i, pp. 30-38, 85-94,
145-149, 4 figs., pis. 5, 6.
Brauer, F. 1869. Betrachtungen iiber die Verwandlung der Insekten im Sinne der Des-
cendenz-Theorie. Verh. zool.-bot. Gesell. Wien, bd. 19, pp. 299-318; bd. 28
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Ganin, M. 1869. Beitrage zur Kenntniss der Entwickelungsgeschichte bei den Insecten.
Zeits. wiss. Zool., bd. 19, pp. 381-451, 3 taf.
Chapman, T. A. 1870. On the Parasitisrn of Rhipiphorus paradoxus. Ann. Mag. Nat.
Hist., ser. 4, vol. 5, pp. 191-198.
Chapman, T. A. 1870. Some Facts towards a Life History of Rhipiphorus paradoxus.
Ann. Mag. Nat. Hist., ser. 4, vol. 6, pp. 314-326, pi. 16.
454 ENTOMOLOGY
Lubbock, J. 1874, 1883. On the Origin and Metamorphoses of Insects. i6 + io8 pp.,
6 pis., 63 figs. London. Macmillan & Co.
Ganin, M. 1876. [Materials for a Knowledge of the Postembryonal Development of
Insects. Warsaw.] (In Russian.) Abstracts: Amer. Nat., vol. 11, 1877, pp.
423-430; Zeits. wiss. Zool., bd. 28, 1877, pp. 386-389.
Riley, C. V. 1877. On the Larval Characters and Habits of the Blister-beetles belonging
to the Genera Macrobasis Lee. and Epicauta Fabr. ; with Remarks on other Species
of the Family Meloidas. Trans. St. Louis Acad. Sc, vol. 3, pp. 544-562, figs. 35-
39, Pl- 5-
Dewitz, H. 1878. Beitrage zur Kenntniss der postembryonalen Gliedmassenbildung bei
den Insecten. Zeits. wiss. Zool., bd. 30, suppl., pp. 78-105, taf. 5.
Packard, A. S. 1878. Metamorphoses [of Locusts]. First Rept. U. S. Ent. Comm., pp.
279-284, pis. 1-3, figs. 19, 20.
Metschnikoff, E. 1883. Untersuchungen iiber die intracellulare Verdauung bei wirbel-
losen Thieren. Arb. zool. Inst. Wien, bd. 5, pp. 141-168, taf. 13, 14.
Viallanes, H. 1883. Recherches sur I'histologie des Insectes et sur les phenomenes histo-
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Ann. Sc. nat. Zool., ser. 6, t. 14, 348 pp., 18 pis.
Kowalevsky, A. 1885. Beitrage zur nachembryonalen Entwicklung der Musciden.
Zool. Anz., jhg. 8, pp. 98-103, 123-128, 153-157.
Schmidt, O. 1885. Metamorphose und Anatomie des mannlichen Aspidiotus nerii.
Archiv Naturg., jhg. 51, bd. i, pp. 169-200, taf. 9, 10.
Witlaczil, E. 1884. Zur Morphologie und Anatomie der Cocciden. Zeits. wiss. Zool.,
bd. 43, PP- 149-174, taf. 5.
Kowalevsky, A. 1887. Beitrage zur Kenntniss der nachembryonalen Entwicklung der
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Van Rees, J. 1888. Beitrage zur Kenntnis der inneren Metamorphose von Musca vomi-
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Hyatt, A., and Anns, J. M. 1890. Insecta. 23 + 300 pp., 13 pis., 223 figs. Boston.
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Bugnion, E. 1891. Recherches sur le developpement post-embryonnaire, I'anatomie, et
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Poulton, E. B. 1891. The External Morphology of the Lepidopterous Pupa: its Relation
to that of the other Stages and to the Origin and History of Metamorphosis.
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Korschelt, E., iind Heider, K. 1892. Lehrbuch der vergleichenden Entwicklungsge-
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Miall, L. C, and Hammond, A. R. 1892. The Development of the Head of Chironomus.
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Pratt, H. S. 1893. Beitrage zur Kenntnis der Pupiparen. Archiv Naturg., jhg. 59, bd.
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Gonin, J. 1894. Recherches sur la metamorphose des Lepidopteres. De la formation des
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Miall, L. C. 1895. The Transformations of Insects. Nature, vol. 53, pp. 153-158.
Hyatt, A., and Anns, J. M. 1896. The Meaning of Metamorphosis. Nat. Sc, vol. 8,
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Kulagin, N. 1897 . Beitrage zur Kenntnis der Entwicklungsgeschichte von Platygaster.
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Packard, A. S. 1897. Notes on the Transformations of Higher Hymenoptera. Journ.
N. Y. Ent. Soc, vol. 4, pp. 155-166, figs. 1-5; vol. 5, pp. 77-87, 109-120, figs. 6-13.
LITERATURE 455
Pratt, H. S. 1897. Tmaginal Discs in Insects. Psyche, vol. 8, pp. 15-30, ii figs.
Packard, A, S. 1898. A Text-Book of Entomology. 17 + 729 pp., 654 figs. New York
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Boas, J. E. V. 1899. Einige Bemerkungen iiber die Metamorphose der Insecten. Zool.
Jahrb., Abth. Syst., bd. 12, pp. 385-402, taf. 20, figs. 1-3.
Lameere, A. 1899. La raison d'etre des metamorphoses chez les Insectes. Ann. Soc.
ent. Belg., t. 43, pp. 619-636.
Perez, C. 1899. Sur la metamorphose des insectes. Bull. Soc. ent. France, pp. 398-402.
Wahl, B. 1901. Ueber die Entwicklung der hypodermalen Imaginalscheiben im Thorax
und Abdomen der Larve von Eristalis Latr. Zeits. wiss. Zool., bd. 70, pp. 171-191,
taf. 9, figs. 1-4. .
Perez, C. 1902. Contribution a I'etude des metamorphoses. Bull. sc. France. Belg., t.
37, pp. 195-427, pis. 10-12, 32 figs.
Deegener, P. 1904, Die Entwicklung des Darmcanals der Insecten wahrend der Meta-
morphose. Zool. Jahrb., Abth. Anat. Ont., bd. 20, pp. 499-676, taf. 33-43-*
Powell, P. B. 1904-05. The Development of Wings of Certain Beetles, and some Studies
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Zool. exp. gen., ser. 5, t. 4, pp. 1-270, pis. 1-16, 162 figs.
Carpenter, G. H. 1921. Insect Transformation. 10 + 282 pp., 1 24 figs., 4 pis. London.
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AQUATIC INSECTS
Dufotir, L. 1849. Des divers modes de respiration aquatique dans les insectes. Compt *
rend. Acad. Sc, t. 29, pp. 763-770. Ann. Mag. Nat. Hist., ser. 2, vol. 6, i85o,pp-
112-118.
Dufour, L. 1852. Etudes anatomiques et physiologiques et observations sur les larves
des Libellules. Ann. Sc. nat. Zool., ser. 3, t. 17, pp. 65-110, 3 pis.
Hagen, H. A. 1853. Leon D ufour uber die Larven der Libellen mit Beriicksichtigung der
friiheren Arbeiten. (Ueber Respiration der Insecten.) Stett. ent. Zeit., bd. 14,
pp. 98-106, 237-238, 260-270, 311-325, 334-346.
Williams, T. 1853-57. On the Mechanism of Aquatic Respiration and on the Structure
of the Organs of Breathing in Invertebrate Animals. Ann. Mag. Nat. Hist., ser.
2, vols. 12-19, 17 pis.
Oustalet, E. 1869. Note sur la respiration chez les nymphes des Libellules. Ann. Sc.
nat. Zool., ser. 5, t. 11, pp. 370-386, 3 pis.
Sharp, D. 1877. Observations on the Respiratory Action of the Carnivorous Water
Beetles (Dytiscidae). Journ. Linn. Soc. Zool., vol. 13, pp. 161-183.
Poletajew, O. 1880. Quelques mots sur les organes respiratoires des larves des Odonates.
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Vayssiere, A. 1882. Recherches sur I'organisation des larves des Ephemerines. Ann.
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Macloskie, G. 1883. Pneumatic Functions of Insects. Psyche, vol. 3, pp. 37S~378.
White, F. B. 1883. Report on the Pelagic Hemiptera. Rept. Sc. Res. Voy. H. M. S.
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Comstock, J. H. 1887. Note on Respiration of Aquatic Bugs. Amer. Nat., vol. 21, pp.
577-578.
Schwedt, E. 1887. Ueber Athmung der Larven und Puppen von Donacia crassipes.
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Amans, P. C, 1888. Comparaisons des organes de la locomotion aquatique. Ann. Sc.
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456 ENTOMOLOGY
Garman, H. 1889. A Preliminary Report on the Animals of the Mississippi Bottoms
near Quincy, Illinois, in August 1888. Bull. 111. St. Lab. Nat. Hist., voL 3, pp.
123-184.
Miall, L. C. 1891. Some Difficulties in the Life of Aquatic Insects. Nature, vol. 44, pp.
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Walker, J. J. 1893. On the Genus Halobates, Esch., and other Marine Hemiptera. Ent.
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Carpenter, G. H. 1895. Pelagic Hemiptera. Nat. Sc, vol. 7, pp. 60-61.
Hart, C. A. 1895. On the Entomology of the Illinois River and Adjacent Waters. Bull.
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Sadones, J. 1895. L'appareil digestif et respiratoire larvaire des Odonates. La Cellule,
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Gilson, G., and Sadones, J. 1896. The Larval Gills of the Odonata. Journ. Linn. Soc.
Zool, vol. 25, pp. 413-418, figs. 1-3.
Comstock, J. H. 1897, 1901. Insect Life. 6 + 349 pp., 18 pis., 296 figs. New York.
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Needham, J. G. 1900. Insect Drift on the Shore of Lake Michigan. Occas. Mem.
Chicago Ent. Soc, vol. i, pp. 1-8, i fig.
Needham, J. G., and Betten, C. 1901. Aquatic Insects in the Adirondacks. Bull.
N. Y. St. Mus , no. 47, PP- 383-612, 36 pis., 42 figs.
Needham, J. G., MacGillivray, A. D., Johamisen, O. A., and Davis, K. C. 1903. Aquatic
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Lutz, F. E. 1913. Factors in Aquatic Environments. Jour. N. Y. Ent. Soc, vol. 21,
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Sleight, C. E. 1913. Relations of Trichoptera to their Environment. Jour. N. Y. Ent.
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Osbum,R. C. 1913. Odonata in Relation to the Hydrophytic Environment. Jour. N. Y.
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Barber, H. G. 1913. Aquatic Hemiptera. Jour. N. Y. Ent. Soc, voL 21, pp. 29-32.
Leng, C. W. 1913. Aquatic Coleoptera. Jour. N. Y. Ent. Soc, vol. 21, pp. 32-42.
Sherman, J. D., Jr. 1913. Some Habits of the Dytiscidae. Journ. N. Y. Ent. Soc, vol.
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U. S. Dept. Agr., Bur. Ent. 13 pp., 7 figs.
Casteel, D. B. 1912. The Behavior of the Honey Bee in Pollen Collecting. Bull. 121,
U. S. Dept. Agr., Bur. Ent. 36 pp., 9 figs.*
Cosens,A. 1912. A Contribution to the Morphology and Biology of Insect Galls. Trans.
Canadian Inst., vol. 9, pp. 297-387, 13 pis., 9 figs.
Thompson, S. M. 1915. An Illustrated Catalogue of American Insect Galls. 116 pp.,
21 pis. Ed. by E. P. Felt. R. I. Hospital Trust Co. Nassau, Rensselaer Co.,
N. Y.
Felt, E. P. 1917. Key to American Insect Galls. Bull. N. Y. State Mus., no. 200.
310 pp., 250 figs., 16 pis.*
Rand, F. V., and Pierce, W. D. 1920. A coordination of our knowledge of insect trans-
mission in plant and animal diseases. Phytopathology, vol. 10, pp. 189-231.*
INSECTS IN RELATION TO OTHER ANIMALS
Aughey, S. 1878. Notes on the Nature of the Food of the Birds of Nebraska. First
Rept. U. S. Ent. Comm., Appendix 2, pp. 13-62.
Forbes, S. A. 1878. The Food of Illinois Fishes. Bull. 111. St. Lab. Nat. Hist., vol. i, no.
2, pp. 71-89.
Forbes, S. A. 1880. The Food of Birds. Trans. 111. St. Hort. Soc, vol. 13 (1879), pp.
120-172.
Forbes, S. A. 1880. On Some Interactions of Organisms. Bull. 111. St. Lab. Nat. Hist.,
vol. I, no. 3, pp. 3-17.
Forbes, S. A. 1880. The Food of Fishes. Bull. 111. St. Lab. Nat. Hist., vol. i, no. 3, pp.
18-65.
Forbes, S. A. 1880. On the Food of Young Fishes. Bull. 111. St. Lab. Nat. Hist., vol. i,
no. 3, pp. 66-79.
Forbes, S. A. 1880. The Food of Birds. Bull. 111. St. Lab. Nat. Hist., vol. i, no. 3, pp.
80-148.
Forbes, S. A. 1883. The Regulative Action of Birds upon Insect Oscillations. Bull.
111. St. Lab. Nat. Hist., vol. i, no. 6, pp. 3-32.
Forbes, S. A. 1883. The Food of the Smaller Fresh- Water Fishes. Bull. 111. St. Lab.
Nat. Hist., vol. i, no. 6, pp. 65-94.
Forbes, S. A. 1883. The First Food of the Common White-Fish. Bull. 111. St. Lab. Nat.
Hist., vol. I, no. 6, pp. 95-109.
Dimmock, G. 1886. Belostomidae and some other Fish-destroying Bugs. Ann. Rept.
Fish Game Comm. Mass., pp. 67-74, i fig.*
Forbes, S. A. 1888. Studies on the Food of Fresh- Water Fishes. Bull. 111. St. Lab. Nat.
Hist, vol. 2 pp. 433-473-
Forbes, S. A. 1888. On the Food Relations of Fresh- Water Fishes: a Summary and
Discussion. Bull. 111. St. Lab. Nat. Hist., vol. 2, pp. 475-538.
Wilcox, E.V. 1892. The Food of the Robin. Bull. Ohio Agr. Exp. Sta., no. 43, pp. 115-
131-
Beal, F. E. L. 1897. Some Common Birds in their Relations to Agriculture. Farmer's
Bull. U. S. Dept. Agric, no. 54, pp. 1-40, figs. 1-22.
Kirkland, A. H. 1897. The Habits, Food and Economic Value of the American Toad.
Bull. Hatch Exp. Sta. Mass. Agr. Coll., no. 46, pp. 3-30, pi. 2.
Judd, S. D. 1899. The EflBciency of Some Protective Adaptations in Securing Insects
from Bir ds. Amer. Nat., vol. 33, pp. 461-484.
464 ENTOMOLOGY
Palmer, T. S. 19C0. A Review of Economic Ornithology. Yearbook U. S. Dept. Agric.
1899, pp. 259-292.
Judd, S, D. 1901. The Food of Nestling Birds. Yearbook U. S. Dept. Agric. 1900, pp.
411-436, pis. 49-53, figs. 48-56.
Forbes, S. A. 1903. Studies of the Food of Birds, Insects and Fishes. Second Ed. Bull.
111. St. Lab. Nat. Hist., vol. i, no. 3.
Weed, C. M., and Dearborn, N. 1903. Birds in their Relations to Man. 8 + 380 pp.,
figs. Philadelphia and London. J. B. Lippincott Co.*
Washburn, F. L. 1918. Injurious Insects and Useful Birds. 18 + 453 pp., 414 figs.,
4 pis. Philadelphia and London. J. B. Lippincott Co.
Undefhill, B. M. 1920. Parasites and Parasitosis of the Domestic Animals. 19 + 379
pp., 172 figs., 8 pis. New York. The Macmillan Co.
INSECTS IN RELATION TO DISEASES
Kanthack, A. A., Durham, H. E., and Blandford, W. F. H. 1898. On Nagana, or Tsetse
fly disease. Proc. Roy. Soc. Lond., vol. 64, pp. 100-118.
Finlay, C. J. 1899. Mosquitoes considered as Transmitters of Yellow Fever and Malaria.
Psyche, vol. 8 pp. 379-384.
Nuttall, G. H. F. 1899. On the role of Insects, Arachnids and Myriapods, as carriers in
the spread of Bacterial and Parasitic Diseases of Man and Animals. A Critical
and Historical Study. Johns Hopk. Hosp. Rept., vol. 8, no. i, 154 pp., 3 pis.
Ross, R. 1899. Life-History of the Parasites of Malaria. Nature, vol. 60, pp. 322-324.
Chiisly, C. 1900. Mosquitoes and Malaria: a summary of knowledge on the subject up
to date; with an account of the natural history of mosquitoes. 9 + 80 pp., 5 pis.
London.
Howard, L. O. 1900. Notes on the Mosquitoes of the United States: giving some account
of their structure and biology, with remarks on remedies. Bull. U. S. Dept. Agric,
Div. Ent., no. 25 (n. s.), 70 pp., 22 figs.
Howard, L. O. 1900. A contribution to the study of the insect fauna of human excrement
(with especial reference to the spread of typhoid fever by flies) . Proc. Wash. Acad.
Sc, vol. 2, pp. 541-604, pis. 30, 31, figs. 17-38.
Ross, R. 1900. Malaria and Mosquitoes. Nature, vol. 61, pp. 522-527.
Ross. R., and Fielding-Otild, R. 1900. Diagrams illustrating the Life-history of the
Parasites of Malaria. Quart. Journ. Micr. Sc, vol. 43 (n. s.), pp. 571-579, pis. 30,
31-
Grassi, B. 1901. Die Malaria-Studien eines Zoologen. 8 + 250 pp., 8 taf. Jena. G.
Fischer.
Howard, L. O. 1901. ^Mosquitoes; how they live; how they carry disease; how they are
classified; how they may be destroj^ed. 15 -f- 241 pp., 50 figs., i pi. New York.
McClure, Phillips & Co.
Sternberg, G. M. 1901. The Transmission of Yellow Fever by Mosquitoes. Pop. Sc.
Mon., vol. 59, pp. 225-241.
■Howard, L. O. 1902. Insects as Carriers and Spreaders of Disease. Year-book U. S.
Dept. Agric. 1901, pp. 177-192, figs. 5-20.
Braxm, M. 1903. Die thierischen Parasiten des Menschen. Rev. Ed. 12-1-360 pp.,
272 figs. Wiirzburg.
Sternberg, G. M. 1903. Infection and Immunity; with special Reference to the Preven-
tion of Infectious Diseases. 5 + 293 pp., 12 figs. New York and London. G. P.
Putman's Sons.
Blanchard, R. 1905. Les ]\Ioustiques, histoire naturelle et medicale. 673 pp., 316 figs.
Paris. De Rudeval.
LITERATURE 465
Austen, E. E. 1903. A Monograph of the Tsetse FHes. 9 + 319 pp., 9 pis. London.
British Museum.
Braun, M. 1906. The Animal Parasites of Man. Trans. Sambon and Theobald. 19 +
453 PP-> 294 figs. New York. Wm. Wood & Co.
Bruce, D. 1907. Trypanosomiasis.- In Osier's Modern Medicine, vol. i, pp. 460-487,
tigs. 31-34, pi. 4. Philadelphia and New York. Lea Bros. & Co.
Calvert, W. J. 1907. Plague. In Osier's Modern Medicine, vol. 2, pp. 760-780.
Philadelphia and New York. Lea Bros. & Co.
Carroll, J. 1907. Yellow Fever. In Osier's Modern Medicine, vol. 2, pp. 736-759.
Philadelphia and New York. Lea Bros. & Co.
Craig, C. F. 1907. The Malarial Fevers. In Osier's Modern Medicine, vol. i, pp. 392-
448, figs. 26-30, pis. 1-3. Philadelphia and New York. Lea Bros. & Co.
Griinberg, K. 1907. Die blutsaugenden Dipteren. 6 + 188 pp. Jena. G. Fischer.
Jackson, T.W. 1907. Tropical Medicine. 8 + 536 pp., 106 figs. Philadelphia. P.
Blakiston's Son & Co.
Laveran, A., and Mesnil, F. 1907. Trypanosomes and Trypanosomiases. Trans. D.
Nabarro. 19 + 538 pp., 81 figs., i pi. London. Bailliere, Tindall & Co.*
Mitchell, E. G. 1907. Mosquito Life. 22 + 281 pp., 54 figs. New York and London.
G. P. Putnam's Sons.
Stephens, J. W. W., and Christophers, S. R. 1908. The Practical Study of Malaria and
Other Blood Parasites. Ed. 3. 18 + 414 pp., 128 figs. London. Williams and
Norgate.
Boyce, R. W. 1909. Mosquito or Man? The Conquest of the Tropical World. 16 +
267 pp., 44 figs. London. John Murray.
Calkins, G. N. 1909. Protozoology. 9 + 349 PP-, 125 figs., 4 pis. New York and
Phila. Lea & Febiger.*
Thimm, C. A. 1909. Bibliography of Trypanosomiasis. 22S pp. London. ^^Sleeping
Sickness Bureau.
Braun, M., and Liihe, M. 1910. A Handbook of Practical Parasitology. Tr. L. Forster.
8 + 208 pp., 100 figs. London. John Bale, Sons & Danielsson.
Doane, R. W. 1910. Insects and Disease. 14 +227 pp., 112 figs., i pi. New York.
Henry Holt & Co.*
Austen, E.E. 1911. A Handbook of the Tsetse-flies (Genus Glossina). 10 + no pp., 24
figs., 10 pis. London. British Museum.
Doane, R. W. 1911, 1912. An Annotated List of the Literature on Insects and Disease.
Journ. Econ. Ent., vol. 4, pp. 386-398; vol. 5, pp. 268-285.
Howard, L. O. 1911. The House Fly; Disease Carrier. 19 + 312 pp., 40 figs., r pi.
New York. F. A. Stokes Co.*
Manson, P. 1911. Tropical Diseases. Ed. 6. 22 + 968 pp., 254 figs., 15 pis.
London and New York. Cassell & Co.
Reed, W., Carroll, J., Gorgas, W. C, and others. 1911. Yellow Fever; a Compilation of
Various Publications. Doc. No. 822, U. S. Senate, 6ist Congress. 250 pp., 7 figs.,
5 pis. Washington. Govt. Printing Office.
Brues, C. T. 1913. The Relation of the Stable Fly (Stomoxys calcitrans) to the Trans-
mission of Infantile Paralysis. Journ. Econ. Ent., vol., 6, pp. 101-109.
Herms, W. B. 1915. Medical and Veterinary Entomology. 12 + 393 PP-. 228 figs.
New York. The Macmillan Co.
Riley, W. A., and Johannsen, O. A. 1915. Handbook of Medical Entomology. 9 + 348
pp., 174 figs. Ithaca, N. Y. Comstock Pub. Co.*
Chandler, A. C. 1918. Animal Parasites and Human Disease. 13 + 570 pp., 254 figs.
New York. John Wiley & Sons, Inc.*
466 ENTOMOLOGY
Pierce, W. D. 1921. Sanitary Entomology, Entomology of Disease, Hygiene and Sanita-
tion. 26 + 518 pp., 88 figs. Boston. R. G. Badger.*
INTERRELATIONS OF INSECTS
Van Beneden, P. J. 1876, Animal Parasites and Messmates. 28 + 274 pp., 83 figs.
New York. D. Appleton & Co.
McCook, H. C. 1877. Mound-making Ants of the Alleghenies, their Architecture and
Habits. Trans. Amer. Ent. Soc, vol. 6, pp. 253-296, figs. 1-13.
Fabre, J. H. 1879-1905. Souvenirs entomologiques. Etudes sur I'instinct et les moeurs
des insectes. 9 Series. Paris. C. Delagrave. Trans, of Ser. I: 1901. Fatre,
J. H. Insect Life. 12 + 320 pp., 16 pis. London and New York. The Mac-
millan Co
Forbes, S. A. 1880. Notes on Insectivorous Coleoptera. Bull. 111. St. Lab. Nat. Hist.,
vol. I, no. 3, pp. 153-169. Second Ed., 1903.
McCook, H. C. 1880. The Natural History of the Agricultural Ant of Te.xas. 310 pp.,
24 pis. Philadelphia. J. B. Lippincott & Co.
Webster, F. M. 1880. Notes upon the Food of Predaceous Beetles. Bull. 111. St. Lab.
Nat. Hist., vol. i, no. 3, pp. 149-152. Second Ed., 1903.
McCook, H. C. 1881. Note on a new Northern Cutting Ant, Atta septentrionalis. Proc.
Acad. Nat. Sc. Phila. 1880, pp. 359-363, i fig.
McCook, H. C. 1881. The Shining Slavemaker. Notes on the Architecture and Habits
of the American Slave-making Ant, Polyergus lucidus. Proc. Acad. Nat. Sc.
Phila. 1880, pp. 376-384, pi. 19.
Lubbock, J. 1882, 1902, 1904. Ants, Bees and Wasps. 19 + 448 pp., 31 figs., 5 pis.
New York. D. Appleton & Co.
McCook, H. C. 1882. The Honey Ants of the Garden of the Gods, and the Occident Ants
of the American Plains. 188 pp., 13 pis. Philadelphia. J. B. Lippincott & Co.
Forbes, S. A. 1883. The Food Relations of the Carabidae and Coccinellidae. Bull. 111.
St. Lab. Nat. Hist., vol. i, no. 6, pp. 33-64.
Cheshire, F. R. 1886. Bees and Bee-keeping. 2 vols. Vol. i, 7 + 336 pp., 8 pis., 71
figs; vol. 2, 652 pp., 127 figs., I pi. London. L. Upcott Gill.
Seitz, A. 1890, 1893, 1894. Allgemeine Biologie der Schmetterlinge. Zool. Jahrb., Abth.
Syst., etc., bd. 5, pp. 281-343; bd. 7, pp. 131-186, 823-851.*
Verhoeff, C. 1892. Beitrage zur Biologie der Hymenoptera. Zool. Jahrb., Abth. Syst.,
etc., bd. 6, pp. 680-754, taf. 30, 31.
Wasmann, E. 1894. Kritisches Verzeichnis der myrmekophUen und termitophilen
Arthropoden. 231 pp. Berlin. F. L. Dames.
Grassi, B., and Sandias, A. 1896-97. The Constitution and Development of the Society
of Termites, etc. Trans, by W. F. H. Blandford. Quart. Journ. Micr. Sc, vol.
39, pp. 245-322, pis. 16-20; vol. 40, pp. 1-75.
Janet, C. 1896. Les Fourmis. Bull. Soc. zool. France, vol. 21, pp. 60-93. Sep., 37 pp.
Paris.
Howard, L. O. 1897. A Study in Insect Parasitism. Bull. U. S. Dept. Agric, Div. Ent.,
tech. ser. no. 5, pp. 1-57, figs. 1-24.
Peckham, G. W., and E. G. 1898. On the Instincts and Habits of the Solitary Wasps.
Bull Wis. Geol. Nat. Hist. Surv., no. 2, sc. ser. no. i, 4 + 245 pp., 14 pis.
Wasmann, E. 1898, Die Gaste der Ameisen und Termiten. Illustr. Zeits. Ent., bd. 3,
I taf.
Benton, F. 1899. The Honey Bee: A Manual of Instruction in Apiculture. Bull. U. S.
Dept. Agric, Div. Ent., no. 1 (n. s.), pp, 1-118, pis. i-n, figs. 1-76.*
Fielde, A. M. 1901. A Study of an Ant. Proc. Acad. Nat. Sc. Phila., vol. 53, pp. 425-
449-
LITERATURE 467
Fielde, A. M. 1901. Further Study of an Ant. Proc. Acad. Nat. Sc. Phila., vol. 53, pp.
521-544-
Wheeler, W. M. 1901. The Compound and Mixed Nests of American Ants. Amer. Nat. ,
vol. 35, pp. 4.31, 513, 701, 791, figs. 1-20.
Enteman, M. M. 1902. Some Observations on the Behavior of the Social Wasps. Pop.
Sc. Men., vol. 61, pp. 339-351-
Fielde, A.M. 1902. Notes on an Ant. Proc. Acad. Nat. Sc. Phila., vol. 54, pp. 599-625.
Dickel, F. 1903. Die Ursachen der geschlechtlichen DifTerenzirung im Bienenstaat.
Archiv. ges. Phys., bd. 95, pp. 66-106, fig. i.
Fielde, A. M. 1903, Supplementary Notes on an Ant. Proc. Acad. Nat. Sc. Phila., vol.
55. PP- 491-495-
Heath, H. 1903. The Habits of California Termites. Biol. Bull., vol. 4, pp. 47-63, figs.
1-3-
Janet, C. 1903. Observations sur les guepes. 85 pp., 30 figs. Paris. C. Naud.
Melander, A. L., and Brues, C. T. 1903. Guests and Parasites of the Burrowing Bee
Halictus. Biol. Bull., vol. 5, pp. 1-27, figs. 1-7.
Fielde, A. M. 1904. Power of Recognition among Ants. Biol. Bull, vol. 7, pp. 227-250,
4 figs-
Fielde, A. M., and Parker, G. H. 1904. The Reactions of Ants to Material Vibrations.
Proc. Acad. Nat. Sc. Phila., vol. 56, pp. 642-650.*
Wheeler, W. M. 1904. A New Type of Social Parasitism among Ants. Bull. Amer.
Mus. Nat. Hist., vol. 20, pp. 347-375.
Emery, C. 1904. Zur Kenntniss des Polymorphismus der Ameisen. Zool. Jahrb., Sup-
plement, bd. 7, pp. 587-610, 6 figs.
Forel, A. 1904. Ueber Polymorphismus und Variation bei den Ameisen. Zool. Jahrb.,
Supplement, bd. 7, pp. 571-586.
Peckham, G. W., and E. G. 1906. Wasps, Social and Solitary. 15 + 311 pp. Boston
and New York. Houghton, Mifflin & Co.
Holmgren, N. 1906. Studien liber sudamerikanische Termiten. Zool. Jahrb., Abt.
Anat. Ont., bd. 23, pp. 521-676, 81 figs.*
Wheeler, W. M. 1906. The Habits of the Tent-building Ant (Cremastogaster lineolata
Say). Bull. Amer. Mus. Nat. Hist., vol. 22, pp. 1-18, pis. 1-6.
Wheeler, W. M. 1906. On the Founding of Colonies by Queen Ants, etc. Bull. Amer.
Mus. Nat. Hist., vol. 22, pp. 33-105, pis. 8-14.
Wheeler, W. M. 1907. The Polymorphism of Ants, with an Account of Some Singular
Abnormalities due to Parasitism. Bull Amer. Mus. Nat. Hist., vol. 23, pp. 1-93,
pis. 1-6.
Wheeler, W. M. 1907. The Fungus-growing Ants of North America. Bull. Amer. Mus.
Nat. Hist., vol. 23, pp. 669-807, pis. 49-53, 31 figs.*
Pricer, J. L. 1908. The Life History of the Carpenter Ant. Biol. Bull, vol. 14, pp. 177-
218, figs. 1-7.*
Donisthorpe, J. K. 1910. Some Experiments with Ants' Nests. Trans. Ent. Soc.
London, pp. 142-150.
Wheeler, W. M. 1910. Ants; their Structure, Development and Behavior. 25 + 663
pp., 286 figs., I pi. New York. Columbia Univ. Press.*
Crawley, W. C. 1912. Parthenogenesis in Worker Ants, with Special Reference to Two
Colonies of Lasius niger Linn. Trans. Ent. Soc. London, 191 1, pp. 657-663.*
Sladen, F. W. L. 1912. The Humble-Bee, its Life-History and How to Domesticate it.
13 -1- 283 pp., 34 figs., 6 pis. London. Macmillan & Co.
Fuller, C. 1915. Observations on Some South African Teimites. Ann. Natal Mus.,
vol. 3, pp. 329-504, 16 figs., pis. 25-35.
468 ENTOMOLOGY
Thompson, C. B. 1917. Origin of the Castes of the Common Termite, Leucotermes
flavipes Kol. Journ. Morph., vol. 30, pp. 83-153, 8 pis.*
Wheeler, W. M. 1918. A study of some ant larvae, with a consideration of the origin and
meaning of the social habit among insects. Proc. Amer. Phil. Soc, vol. 57, pp.
293-343, 12 figs.
Thompson, C. B. 1919. The Development of the Castes of Nine Genera and Thirteen
Species of Termites. Biol. Bull., vol. 36, pp. 379-398.
Thompson, C. B., and Snyder, T. E. 1919. The Question of the Phylogenetic Origin of
the Termite Castes. Biol. Bull., vol. 36, pp. 1 15-132.
Wheeler, W. M. 1919. The parasitic Aculeata, a study in evolution. Proc. Amer. Phil.
Soc, vol. 58, pp. 1-40.
Banks, N., and Snyder, T. E. 1920. .\ Revision of the Nearctic Termites, with Notes on
Biology and Geographic Distribution. Bull. U. S. Nat. Mus., no. 108, 8 + 228
pp., 70 figs., 35 pis.*
Wheeler, W. M. 1921. A Study of Some Social Beetles in British Guiana and of Their
Relations to the Ant-plant Tachigalia. Zoologica, vol. 3, pp. 35-126, 5 pis.*
INSECT BEHAVIOR
Pouchet, G. 1872. De I'influence de la lumiere sur les larves de dipteres privees d' organes
e.xterieurs de la vision. Rev. Mag. Zool, ser. 2, t. 23, pp. 110-117, etc., pis. 12-16.
Fabre, J. H. 1879-1905. Souvenirs entomologiques. Etudes sur I'instinct et les moeurs
des insectes. 9 Series. Paris. C. Delagrave. Trans, of Ser. I: 1901. Fabre,
J. H. Insect Life. 12 +320 pp., 16 pis. London and New York. The Mac-
millan Co.
Lubbock, J. 1882, 1884. Ants, Bees and Wasps. 19 + 448 pp., 31 figs., 5 pis. New
York. D. Appleton & Co.
Graber, V. 1884. Grundlinien zur Erforschung des Helligkeits- und Farbensinnes der
Tiere. 8 + 322 pp. Prag und Leipzig.
Romanes, G. J. 1884. Animal Intelligence. 14 + 520 pp. New York. D. Appleton
& Co.
Lubbock, J. 1888. On the Senses, Instincts and Intelligence of Animals, with Special
Reference to Insects. 29 + 292 pp., 118 figs. New York. D. Appleton & Co.
Plateau, F. 1889. Recherches e.xperimentales sur la Vision chez les Arthropodes. Mem.
cour. Acad. roj-. Belgique, t. 43, pp. 1-91.
Eimer, G. H. T. 1890. Organic Evolution as the Result of the Inheritance of Acquired
Characters according to the Laws of Organic Growth. 28 + 435 pp. Trans, by
J. T. Cunningham. London and New York. Macmillan & Co.
Loeb, J. 1890. Der Heliotropismus der Thiere und seine Uebereinstimmung mit dem
Heliotropismus der Pflanzen. 118 pp. Wiirzburg.
Seitz, A. 1890. Allgemeine Biologie der Schmetterlinge. Zool. Jahrb., Abth. Syst., bd.
5, pp. 281-343.
Exner, S. 1891. Die Physiologie der facettirten Augen von Krebsen und Insecten. 8 +
206 pp., 8 taf., 23 figs. Leipzig und Wien.
Loeb, J. 1891. Ueber Geotropismus bei Thieren. Arch. ges. Phys., bd. 49, pp. 175-189,
figs.
Morgan, C. Lloyd. 1891. Animal Life and Intelligence. 13 + 512 pp., 40 figs. Boston.
Ginn & Co.
James, W. 1893. The Principles of Psychology. 2 vols. 18 + 1393 pp., 94 figs. New
' York. Henry Holt & Co.
Loeb, J. 1893. Ueber kunstliche Umwandlung positiv heliotropischer Thiere in negativ
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LITERATURE 469
Baldwin, J. M. 1896. Heredity and Instinct. Science, vol. 3 (n. s.), pp. 438-441, 558-
561.
Morgan, C. Lloyd, 1896. Habit and Instinct. 351 pp. London and New York. E.
Arnold.
Davenport, C. B. 1897, 1899. E.xperimental Morphology. 2 Pts. 32 + 508 pp, 140
figs. New York and London. The Macmillan Co.
Loeb, J. 1897. Zur Theorie der physiologischen Licht- und Schwerkraftwirkungen.
Arch. ges. Phys., bd. 64, pp. 439-466.
Bethe, A. 1898. Durfen wir den Ameisen und Bienen psychische Qualitaten zuschreiben?
Archiv ges. Phys., bd. 70. pp. 15-110, taf. i, 2, 5 figs.
Peckham, G. W., and E. G. 1898. On the Instincts and Habits of the Solitary Wasps.
Bull. Wis. Geol. Nat. Hist. Surv., no. 2, so. ser. no. i. 4 + 245 pp., 14 pis.
Verwom, M. 1899. General Physiology. An Outline of the Science of Life. Trans.
by F. S. Lee. 16 + 615 PP-> 285 figs. London and New York. Macmillan & Co.
Wasmann, E. 1899. Die psychischen Fahigkeiten der Ameisen. Zoologica, heft 26.
6 + 132 pp., 3 taf. Stuttgart. E. Nagele.
Wheeler, W. M. 1899. Anemotropism and Other Tropisms in Insects. Arch. Entw. Org.,
bd. 8, pp. 373-381.
Whitman, C. O. 1899. Animal Behavior. Biol Lect., Marine Biol. Lab., Woods Hole,
Mass., 1898, pp. 285-338. Boston. Ginn & Co.
Loeb, J. 1900. Comparative Physiology of the Brain and Comparative Psychology. 309
pp., 39 figs. New York, G. P. Putnam's Sons. London, J. Murray.*
Morgan, C. Lloyd. 1900. Animal Behaviour. 8 + 344 pp., 26 figs. London. E.
Arnold.
Radl, E. 1901. Ueber den Phototropismus einiger Arthropoden. Biol. Centralb., bd.
21, pp. 75-86.
Radl, E. 1901. Untersuchungen iiber die Lichtreactionen der Arthropoden. Arch. ges.
Phys., bd. 87, pp. 418-466.
Enteman, M. M. 1902. Some Observations on the Behavior of the Social Wasps. Pop.
Sc. Mon., vol. 61, pp. 339-351-
Weismann, A. 1902. Vortrage iiber Descendenztheorie. 2 vols. 12 + 456 pp., 95 figs.;
6 + 462 pp., 3 pis., 36 figs. Jena. G. Fischer. See pp. 159-181.
Kathariner, L. 1903. Versuche iiber die Art der Orientierung bei der Honigbiene. Biol.
Centralb., bd. 23, pp. 646-660, i fig.
Morgan, T. H. 1903. Evolution and Adaptation. 13 + 470 pp., 5 figs. New York and
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Parker, G. H. 1903. The Phototropism of the Mourning-cloak Butterfly, Vanessa antiopa
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Fielde, A. M., and Parker, G. H. 1904. The Relations of Ants to Material Vibrations.
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Forel, A. 1904. The Psychical Faculties of Ants and some other Insects. Ann. Rept.
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Berlin, 1901, pp. 141-169.
Jennings, H. S. 1904. Contributions to the Study of the Behavior of Lower Organisms.
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Hartman, C. 1906. Observations on the Habits of some Solitary Wasps of Texas. Bull.
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Holmes, S. J. 1905. The Reactions of Ranatra to Light. Journ. Comp. Neur. Psych.,
vol. 15, pp. 305-349, figs. 1-6.
470 ENTOMOLOGY
Loeb, J. 1905. Studies in General Physiology. 2 vols. 24 + 782 pp., 162 figs. Univ.
Chicago Decenn. Publ., ser. 2, vol. 15, pts. i, 2.
Wasmann, E. 1905. Comparative Studies in the Psychology of Ants and of Higher Ani-
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Cole, W. H. 1917. The Reactions of Drosophila ampelophila Loew to Gravity, Centrifu-
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Mclndoo, N. E. 1917. Recognition Among Insects. Smiths. Misc. Coll., vol. 68, no.
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Bouvier, E. L. 1918. La Vie psychique des Insectes. 300 pp., 16 figs. Paris. Ernest
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Loeb, J. 1918. Forced Movements, Tropisms,. and Animal Conduct. 209 pp., 42 figs.
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Princeton. Univ. Press.
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GEOGRAPHICAL DISTRIBUTION
Darwin, C. 1859,1869. On the Origin of Species by means of Natural Selection. Pp-
II +440. New York. D. Appleton & Co. See pp. 302-357.
LeConte, J. L. 1859. The Coleoptera of Kansas and Eastern New Mexico. Smithson.
Contrib., vol. 11, 6 -|- 58 pp., 2 pis., map.
Bates, H. W. 1864. The Naturalist on the River Amazons. 12 -|- 466 pp., figs. London.
J. Murray.
LITERATURE 47I
Wallace, A. R. 1865. On the Phenomena of Variation and Geographical Distribution as
illustrated by the Papilionidae of the Malayan Region. Trans. Linn. Soc. Zool.,
vol. 25, pp. 1-71, pis. 1-8.
"Wallace, A. R. 1869. The Malay Achipelago. 12 + 638 pp., 51 figs., 10 maps. New
York. Harper & Bros.
Murray, A, 1873. On the Geographical Relations of the Chief Coleopterous Faunae.
Journ. Linn. Soc. Zool, vol. 11, pp. 1-89.
Belt, T. 1874, 1888. The Naturalist in Nicaragua. 32 + 403 PP-j figs. London. J.
MuTTa.y; E. Bumpus.
Wallace, A. R. 1876. The Geographical Distribution of Animals. 2 vols. Vol. i, 21 +
503 pp., 13 pis., 5 maps; vol. 2, 8 + 607 pp., 7 pis., 2 maps. New York. Harper
& Bros.
Semper, K. 1881. Animal Life as affected by the Natural Conditions of Existence. 1 6 +
472 pp., 106 figs., 2 maps. New York. D. Appleton & Co.
Wallace, A. R. 1881. Island Life, or the Phenomena and Causes of Insular Faunas and
Floras, etc. 16 + 522 pp., 26 maps and figs. New York. Harper & Bros.
Gill, T. 1884. The Principles of Zoogeography. Proc. Biol. Soc. Wash., vol. 2, pp. 1-39.
Forbes, H. O. 1886. A Naturalist's Wanderings in the Eastern Archipelago. 19 + S36
pp., figs., pis., maps. New York. Harper & Bros.
Schwarz, E. A. 1888. The Insect Fauna of Semitropical Florida, with Special Regard to
the Coleoptera. Ent. Amer., vol. 4, pp. 165-175.
Merriam, C. H. 1890. Results of a Biological Survey of the San Francisco Mountain
Region and Desert of the Little Colorado, Arizona. U. S. Dept. Agric, Div.
Ornith. Mamm., N. A. Fauna, no. 3. 6 + 136 pp., 13 pis., 5 maps, 2 figs.
Schwarz, E. A. 1890. On the Coleoptera common to North America and other Countries.
Proc. Ent. Soc. Wash., vol. i, pp. 182-194.
Seitz,A. 1890,1893,1894. AUgemeine Biologic der Schmetterlinge. Zool. Jahrb., Abth.
Syst, etc., bd. 5, pp. 281-343; bd. 7, pp. 131-186, 823-851.*
Trouessart, E. L. 1890. La Geographie Zoologique. 11 +338 pp., 63 figs., 2 maps.
Paris.
Wallace, A, R. 1890. A Narrative of Travels on the Amazon and Rio Negro, etc. Ed. 3.
14 + 363 pp., 16 pis. London, New York and Melbourne. Ward, Lock & Co.
Bates, H. W. 1892. The Naturalist on the River Amazons. Reprint. 89 + 395 pp.,
figs. London. J. Murray.
Distant, W. L. 1892. A Naturalist in the Transvaal. 16 + 277 pp., pis. figs. London.
R. H. Porter.
Hudson, W.H. 1892. The Naturalist in La Plata. 8 + 388 pp., figs. London. Chap-
man & Hall.
Webster, F. M. 1892. Modern Geographical Distribution of Insects in Indiana. Proc.
Ind. Acad, Sc, pp. 81-88, map.
Merriam, C. H. 1893. The Geographic Distribution of Life in North American, with
special Reference to the Mammalia. Smithson. Rept. 1891, pp. 365-415. From
Proc. Biol. Soc. Wash., vol. 7, pp. 1-64.
Elwes, H. J. 1894. The Geographical Distribution of Butterflies. Trans. Ent. Soc.
London, Proc, pp. 52-84.
Hamilton, J. 1894. Catalogue of the Coleoptera common to North America, Northern
Asia and Europe, with Distribution and Bibliography. Trans. Amer. Ent. Soc,
vol. 21, pp. 345-416 + 19.
Merriam, C. H. 1894. Laws of Temperature Control of the Geographic Distribution of
Terrestrial Animals and Plants. Nat. Geogr. Mag., vol. 6, pp. 229-238, 3 maps.
Scudder, S. H. 1894. The Effect of Glaciation and of the Glacial Period on the Present
Fauna of North America. Amer. Journ. Sc, sen 3, vol. 48, pp. 179-187.
472 ENTOMOLOGY
Webster, F. M. 1894. Some Insect Immigrants in Ohio. Bull. Ohio Agr. Exp. Sta.,
ser. 2, vol. 6, no. 51 (1893), pp. 118-129, figs. 17, 18.
Whymper, E. 1894. Travels amongst the Great Andes of the Equator. 24 + 456 pp.,
20 pis., 4 maps, 118 figs. New York. C. Scribner's Sons. 1891. Suppl. Ap-
pendix. 22 + 147 pp., figs. London. J. Murray.
Beddard, F. E. 1895. A Text-book of Zoogeography. 8-1-246 pp., 5 maps. Cambridge,
England. University Press.
Howard, L. O. 1895. Notes on the Geographical Distribution within the United States
of certain Insects injuring Cultivated Crops. Proc. Ent. Soc. Wash., vol. 3, pp.
219-226.
Webster, F. M. 1895. Notes on the Distribution of some Injurious Insects. Proc. Ent.
Soc. Wash., vol. 3, pp. 284-290.
Webster, F. M. 1896. The Probable Origin and Diffusion of Blissus leucopterus and
Murgantia histrionica. Journ. Cine. Soc. Nat. Hist., vol. 18, pp. 141-155, fig. i,
pl- 5.
Carpenter, G. H. 1897. The Geographical Distribution of Dragon-flies. Proc. Roy.
Dublin Soc, vol. 8, pp. 439-468, pl. 17.
Heilprm, A. 1897. The Geographical and Geological Distribution of Animals. 12-1-435
pp., map. New York. D. Appleton & Co.
Sairille-Kent, W. 1897. The Naturalist in Australia. 15 + 302 pp., 50 pis., 104 figs.
London. Chapman & Hall.
Webster, F. M. 1897. Biological Effects of Civilization on the Insect Fauna of Ohio.
Fifth Ann. Rept. Ohio St. Acad. Sc, pp. 32-46, 2 figs.
Merriam, C. H. 1898. Life Zones and Crop Zones of the United States. Bull. U. S.
Dept. Agric, Div. Biol. Surv., no. 10, pp. 1-79, map.
Webster, F. M. 1898. The Chinch Bug. Bull. U. S. Dept. Agric, Div. Ent., no. 15
(n. s.), 82 pp., 19 figs. (See pp. 66-82.)
Semon, R. 1899. In the Australian Bush and on the Coast of the Coral Sea, etc. 15 -f-
552 pp., 4 maps, 86 figs. London and New York. Macmillan & Co.
Tower, W. L. 1900. On the Origin and Distribution of Leptinotarsa decem-lineata Say,
and the Part that some of the Climatic Factors have played in its Dissemination.
Proc. Amer. Ass. Adv. Sc, vol. 49, pp. 225-227.
Adams, C. C. 1902. Postglacial Origin and Migrations of the Life of tlie Northeastern
United States. Journ. Geogr., vol. i, pp. 303-310, 352-357; rnap.
Adams, C. C. 1902. Southeastern United States as a Center of Geographical Distribution
of Flora and Fauna. Biol. Bull, vol. 3, pp. 115-131.*
Tutt, J. W. 1902. The Migration and Dispersal of Insects. 132 pp. London. E. Stock.
Webster, F. M. 1902. The Trend of Insect Diffusion in North America. Thirty-second
Ann. Rept. Ent. Soc. Ontario (1901), pp. 63-67, maps 1-3.
Webster, F. M. 1902. Winds and Storms as Agents in the Diffusion of Insects. Amer.
Nat., vol. 36, pp. 795-801.
Webster, F. M. 1903. The Diffusion of Insects in North America. Psyche, vol. 10, pp.
47-58, pl. 2.
Jacobi, A. 1904. Tiergeographie. 152 pp., 2 maps. Leipzig.
Morse, A. P. 1904. Researches on North American Acridiidae. Publ. No. 18, Carnegie
Inst. Wash. 55 pp., 8 pis., 13 figs.
Adams, C. C. 1909. The Coleoptera of Isle Royale, Lake Superior, and their Relation to
the North American Centers of Dispersal. In Adams' Ecol. Survey. Rept. Univ.
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Shelford, V. E. 1911. Physiological Animal Geography. Journ. Morph., vol. 22, pp.
551-618, 19 figs.
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609-618, 7 figs.
LITERATURE 473
GEOLOGICAL DISTRIBUTION
Herr, O. 1847-53. Die Insectenfauna der Tertiargebilde von ffiningen und von Radoboj
in Croatien. 3 Th. 644 pp., 40 taf. Leipzig. From Neue Denks. schweiz.
Gesell. Naturw., bd. 8, 11, 13.
Scudder, S. H. 1880. The Devonian Insects of New Brunswick. Ajin. Mem. Bost. See.
Nat. Hist., 41 pp., I pi.
Scudder, S. H. 1882. A Bibliography, of Fossil Insects. Bibl. Contrib. Libr. Harv. Univ. ,
no. 13. 47 pp. Cambridge, Mass.*
Scudder, S. H. 1885. The Earliest Winged Insects of America: a Re-e.xamination of the
Devonian Insects of New Brunswick, etc. 8 pp., i pi., 2 figs. Cambridge, Mass.
Scudder, S. H. 1885. Systematische Uebersicht der fossilen Myriopoden, Arachnoideen
und Insekten. In K. A. Zittel: Handbuch der Palaeontologie, abth. i, bd. 2, pp.
721-831, figs. 894-1109. Trans. 190c: C. R. Eastman. Text-Book of Palaeon-
tology, vol. I, pp. 682-691, figs. ir4i-i476. London and New York. Macmillan
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Scudder, S. H. 1886. The Cockroach of the Past. In L. C. Miall and A. Denny: The
Structure and Life-History of the Cockroach, pp. 205-220, figs. 1 19-1 25. London
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Scudder, S. H. 1886. Systematic Review of our Present Knowledge of Fossil Insects.
Bull. U. S. Geol. Surv., no. 31, 128 pp. Washington.
Scudder, S. H. 1889. The Fossil Butterflies of Florissant. Eighth Ann. Rept. Dir. U. S.
Geol. Surv., pp. 433-474, pi. 53. Washington.
Scudder, S. H. 1890. The Work of a Decade upon Fossil Insects. Psyche, vol. 5, pp.
287-295.
Scudder, S. H. 1890, A Classed and Annotated Bibliography of Fossil Insects. Bull.
U. S. Geol. Surv., no. 69, loi pp. Washington.*
Scudder, S. H. 1890. The Tertiary Insects of North America. U. S. Geol. Surv. Terr.,
vol. 13, 734 pp., 28 pis., I map, 3 figs. Washington.
Scudder, S. H. 1891. Index to the Known Fossil Insects of the World, including Myria-
pods and Arachnids. Bull. U. S. Geol. Surv., no. 71, 744 PP- Washington.*
Scudder, S. H. 1892. Some Insects of Special Interest from Florissant, Colorado, and
other Points in the Territories of Colorado and Utah. Bull. U. S. Geol. Surv., no.
93, 35 PP-, 3 pls- Washington.
Scudder, S. H. 1893. Insect Fauna of the Rhode Island Coal Field. Bull. U. S. Geol.
Surv., no. loi, 27 pp., 2 pis. Washington.
Scudder, S. H. 1893. The American Tertiary Aphidse, with a List of the Known Species
and Tables for their Determination. Thirteenth Ann. Rept. U. S. Geol. Surv., pt.
2, pp. 341-372, pis. 102-106. Washington.
Scudder, S. H. 1893. Tertiary Rhynchophorous Coleoptera of the United States. Mon-
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Brongniart, C. 1894. Recherches pour servir a I'histoire des insectes fossiles des temps
primaires, etc. 2 vols. 537 pp., 37 pis. St. Etienne.
Scudder, S. H. 1894. Tertiary Tipulidse, with Special Reference to those of Florissant,
Colorado. Proc. Amer. Phil. Soc, vol. 32, 83 pp., 9 pis.
Scudder, S. H. 1896. Revision of the American Fossil Cockroaches, with Descriptions of
New Forms. Bull. U. S. Geol. Surv., no. 124, 176 pp., 12 pis. Washington.
Goss, H. 1900. The Geological Antiquity of Insects. Ed. 2. 4 + 52 PP. London.
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Scudder, S. H. 1900. Adephagous and Clavicorn Coleoptera from the Tertiary Deposits
at Florissant, Colorado, etc. Monogr. U. S. Geol. Surv., vol. 40, 148 pp-, n pls.
Washington.
474 ENTOMOLOGY
Scudder, S. H. 1900. Canadian Fossil Insects. 4. Additions to the Coleopterous Fauna
of the Interglacial Clays of the Toronto District, etc. Contrib. Can. Pal., Geol.
Surv. Can., vol. 2, pp. 67-92, pis. 6-15. Ottawa.
Handlirsch, A. 1908. Die Fossilen Insekten und die Phylogenie der Rezenten Formen.
Ein Handbuch fur Palaontologen und zoologen. 49 + 1430 pp., 14 fig?., 51 pis.,
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Handlirsch, A. 1920,1921. Palaeontologie. In Schroder: Handbuch der Entomologie,
bd. 3, pp. 117-306, figs. 52-237.*
INSECT ECOLOGY
Davenport, C. B. 1897, 1899. Experimental Morphology. 2 Pts. 29 + 508 pp., 140
figs. New York and London. The Macmillan Co.*
Chittenden, F. H. 1900. Insects and the Weather: Observations During the Season of
1899. Bull. U. S. Dept. Agric, Div. Ent., no. 22 (n. s.), pp. 51-64.
Morgan, T. H. 1903. Evolution and Adaptation. 13 + 470 pp., 7 figs. New York.
The Macmillan Co.
Morse, A. P. 1904. Researches on North American Acridiidae. 55 pp., 13 figs., 8 pis.
Carnegie Inst. Washington.
Clements, F. E. 1905. Research Methods in Ecology. 17 + 334 pp., 85 figs. Lincoln,
Neb. University Pub. Co.*
Hart, C. A., and Gleason, H. A. 1907. On the Biology of the Sand Areas of Illinois.
BuU. 111. State Lab. Nat. Hist., vol. 7, pp. 137-272, pis. 8-23.*
Herms, W. B, 1907. An Ecological and Experimental Study of Sarcophagidae with
Relation to Lake Beach Debris. Journ. Exp. 2k)ol., vol. 4, pp. 45-83, 7 figs.*
Morgan, T. H. 1907. Experimental Morphology. 12 + 454 pp., 25 figs. New York.
The Macmillan Co.
Morse, A. P. 1907. Further Researches on North American Acridiidse. 54 pp., 9 pis..
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Shelford, V. E. 1907. Preliminary Note on the Distribution of the Tiger Beetles (Cicin-
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Sanderson, E. D. 1908. The Relation of Temperature to the Hibernation of Insects.
Journ. Econ. Ent., vol. i, pp. 56-65, 2 figs.
Sanderson, E. D. 1908. The Influence of Minimum Temperatures in Limiting the
Northern Distribution of Insects. Journ. Econ. Ent., vol. i, pp. 245-262, 7 maps.
Warming, E. 1909. Oecology of Plants. An Introduction to the Study of Plant-
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Bachmetjew, P. 1910. Experimentelle entomologische Studien. 10 + 944 + 108 pp..
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Sanderson, E, D. 1910. The Relation of Temperature to the Growth of Insects. Journ .
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Doten, S. B. 1911. Concerning the Relation of Food to Reproductive Activity and
Longevity in Certain Hymenopterous Parasites. Techn. Bull. Agr. Exp. Sta.
Univ. Nevada, no. 78, 30 pp., 10 pis.
Shelford, V. E. 1911. Ecological Succession. III. A Reconnaissance of its Causes in
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Watson, J. R. 1911. A Contribution to the Study of the Ecological Distribution of the
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Riley, C. F. C. 1912. Observations on the Ecology of Dragon-fly Nymphs: Reactions to
Light and Contact. Ann. Ent. Soc. Amer., vol. 5, pp. 273-292.*
LITERATURE 475
Shelford, V. E. 1912. Ecological Succession. IV. Vegetation and the Control of Land
Animal Communities. Biol. Bull., vol. 23, pp. 59-99, figs. 1-6.*
Shelford, V. E. 1912. Ecological Succession. V. Aspects of Physiological Classifica-
tion. Biol. Bull., vol. 23, pp. 331-370.*
Adams, C. C. 1913. Guide to the Study of Animal Ecology. 12 + 183 pp., 7 figs. New
York. The Macmillan Co.*
Cameron, A. E. 1913. General Survey of the Insect Fauna of the Soil within a Limited
Area near Manchester. Journ. Econ. Biol., vol. 8, pp. 159-204, 2 pis.* '
Headlee, T. J. 1913. Some Facts Regarding the Influence of Temperature and Moisture
Changes on the Rate of Insect Metabolism. Science, n. s., vol. 36, p. 310.
Shelford, V. E. 1913. Animal Communities in Temperate America. A Study in Animal
Ecology. 13+362 pp., 306 figs., 9 diagrams, 2 maps. Chicago. Univ.
Chicago Press.*
Shelford, V. E. 1913. The Reactions of Certain Animals to Gradients of Evaporating
Power of Air. A Study in Experimental Ecology. Biol. Bull.,vol. 25, pp. 79-120.*
Vestal, A. G. 1913. Local Distribution of Grasshoppers in Relation to Plant Associations.
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Vestal, A. G. 1913. An Associational Study of Illinois Sand Prairie. Bull. 111. State Lab.
Nat. Hist., vol. 10, pp. 1-96, pis. 1-5.*
Baxmiberger, J. P. 1914. Studies in the Longevity of Insects. Ann. Ent. Soc. Amer.,
vol. 7, pp. 323-353-*
Headlee, T. J. 1914. Some Data on the Effect of Temperature and Moisture on the Rate
of Insect Metabolism. Journ. Econ. Ent., vol. 7, pp. 413-417.
Krogh, A. 1914. On the influence of the temperature on the rate of embryonic develop-
ment. Zeits. allgem. Phys., bd. 16, pp. 163-177, figs. 1-8.
Krogh, A. 1914. On the rate of development and CO2 production of chrysalides of
Tenebrio molitor at different temperatures. Zeits. allgem. Phys., bd. i6, pp.
178-190, figs. 1-3.
Parks, T. H. 1914. Effect of Temperature upon the Oviposition of the Alfalfa Weevil
(Phytonomus posticus Gyllenhal). Journ. Econ. Ent., vol. 7, pp. 417-421, 3 figs.
Peairs,L. M. 1914. The Relation of Temperature to Insect Development. Journ. Econ.
Ent., vol. 7, pp. 174-179, figs. 10-15.
Shelford, V. E. 1914. The Importance of the Measure of Evaporation in Economic
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Shelford, V. E. 1914. An Experimental Study of the Behavior Agreement among the
Animals of an Animal Community. Biol. Bull., vol. 26, pp. 294-315, figs. 1-41.*
Vestal A. G. 1914. Internal Relations of Terrestrial Associations. Amer. Nat., vol.
48, pp. 413-445-
Weiss, H. B. 1914. Thermal Conductivity of Cocoons. Psyche, vol. 21, pp. 45-5°-
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Bueno, J. R. de la T. 1916. Aquatic Hemiptera. A Study in the Relation of Structure
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Rau, P. and N. 1916. The Sleep of Insects; an Ecological Study. Ann. Ent. Soc.
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Baumberger, J. P. 1917. Hibernation: a Periodical Phenomenon. Ann. Ent. Soc.
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Elwyn, A. 1917. Effect of Humidity on Pupal Duration and on Pupal Mortality of
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Headlee, T. J. 1917. Some Facts Relative to the Influence of Atmospheric Humidity on
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476 ENTOMOLOGY
Loeb, J., and Northrop, J. H. 1917. On the Influence of Food and Temperature upon the
Duration of Life. Journ. Biol. Chem., vol. 32, pp. 103-121.
Tillyat'd, R. J. 1917. The Biology of Dragonflies. 12 + 396 pp., 188 figs. Cambridge.
University Press.
Ely, C. R. 1918. Recent Entomological Chemistry and Some Notes concerning the
Food of Insects. Proc. Ent. Soc. Washington, vol. 20, pp. "12-18.
Headlee, T. J. 1918. Climate and Insect Investigations. Rept. Dept. Ent., N. J. Agr.
E.xp. Sta., 191 7, pp. 442-445-
Shelford, V. E. 1918. Physiological Problems in the Life-Histories of Animals with
Particular Reference to their Seasonal Appearance. Amer. Nat., vol. 52, pp. 129-
154.*
Baumberger, J. P. 1919. A nutritional study of insects with special reference to micro-
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Riley, C. F. C. 1919. Some Habitat Responses of the Large Water-Strider, Gerris
remigis Say. Amer. Nat. vol. 53, pp. 394-414; 483-505.
Brues, C. T. 1920, The Selection of Food-Plants by Insects, with Special Reference to
Lepidopterous Larvae. Amer. Nat, vol. 54, pp. 313-332.
Dozier, H. L. 1920. An Ecological Study of Hammock and Piney Woods Insects in
Florida. Ann. Ent. Soc. Amer., vol. 13, pp. 325-380, 22 figs.*
Pannan, D. C. 1920. Observations on the Effect of Storm Phenomena on Insect Activity.
Journ. Econ. Ent., vol. 13, pp. 339-343-
Peterson, A. 1920. Some Studies on the Influence of Environmental Factors on the
Hatching of the Eggs of Aphis avenae Fabricius and Aphis pomi DeGeer. Ann.
Ent. Soc. Amer., vol. 13, pp. 391-400, pi. 31.*
Riley, C. F. C. 1919. Some Habitat Responses of the Large Water-Strider, Gerris
remigis Say. Amer. Nat., vol. 52, pp. 394-631, figs. 1-6.*
Riley, C. F. C. 1920. Migratory Responses of Water-Striders during Severe Droughts.
Bull. Brooklyn Ent. Soc, vol. 15, pp. i-io.
Claassen, P. W. 1921. Typha Insects: Their Ecological Relationships. Cornell Univ.
Agr. Exp. Sta., Memoir 47, pp. 459-529, pis. 39-48.*
Craighead, F. C. 1921. Hopkins Host-Selection Principle as Related to Certain Ceram-
bjxid Beetles. Journ. Agr. Res., vol. 22, pp. 189-220.
Headlee, T. J. 1921. The Response of the Bean Weevil to Different Percentages of
Atmospheric Moisture. Journ. Econ. Ent, vol. 14, pp. 264-268, fig. 5.
Livingston, B. E., and Shreve, F. 1921. The Distribution of Vegetation in the United
States, as Related to Climatic Conditions. Carnegie Inst. Washington, Pub.
No. 284, 16 + 590 pp.^ 74 figs., 73 pis.*
Ping, C. 1921. The Biology of Ephydra subopaca Loew. Cornell Univ. Agr. Exp. Sta.,
Memoir 49, pp. 557-616, pis. 54-S7-*
Riley, C. F. C. 1921. Distribution of the Large Water-Strider, Gerris remigis Say,
throughout a River System. Ecology, vol. 2, pp. 32-36, figs. 1-3.
INSECTS IN RELATION TO MAN
Harris, T. W. 1862. A Treatise on Some of the Insects Injurious to Vegetation. Third
Ed. II -f 640 pp., 278 figs., 8 pis. Boston.
Lintner, J. A. 1882. Importance of Entomological Study, etc. First Ann. Rept. Inj.
Ins., pp. 1-80, figs. 1-12.
Saunders, W. 1883. Insects Injurious to Fruits. 436 pp., 440 figs. Philadelphia. J. B.
Lippincott & Co.
Packard, A. S. 1889. Guide to the Study of Insects. Ed. 9. 12 + 715 pp., 668 figs.,
15 pis. New York. Henry Holt & Co.
LITERATURE 477
Howard, L. O. 1894. A Brief Account of the Rise and Present Condition of Official Eco-
nomic Entomology. Insect Life, vol. 7, pp. 55-107.
Sempers, F. W. 1894. Injurious Insects and the Use of Insecticides. 10 + 216 pp., i pi.,
184 fijis. Philadelphia. W. A. Burpee & Co.
Smith, J. B. 1896. Economic Entomology for the Farmer and Fruit-Grower, etc. Pp
12 + 1 1-48 1, 483 figs. Philadelphia. J. B. Lippincott Co.
Howard, L. O. 1899. The Economic Status of Insects as a Class. Science, vol. 9 (n. s.)
pp. 233-247.
Theobald, F. V. 1899. A Text-Book of Agricultural Zoology. 17 + 511 pp., 225 figs
Edinburgh and London. Wm. Blackwood & Sons.
Howard, L. O. 1900. Progress in Economic Entomology in the United States. Yearbook
U. S. Dept. Agric, 1899, pp. 135-156, pi. 3-
Sanderson, E. D. 3902. Insects Injurious to Staple Crops. 10 + 295 pp., 163 figs
New York. John Wiley & Sons.
Lodeman, E. G. 1903. The Spraying of Plants. 17 + 399 pp., 92 figs. New York
The Macmillan Co.*
Chittenden, F. H. 1907. Insects Injurious to Vegetables. 14 -f 262 pp., 163 figs,
New York. Orange Judd Co.*
Johnson, W. G. 1908. Fumigation Methods. 16 + 313 pp., 83 figs. New York
Orange Judd Co.
Smith, J. B. 1909. Our Insect Friends and Enemies. 314 pp., 121 figs. Philadelphia.
J. B. Lippincott Co.
O'Kane, W. C. 1912. Injurious Insects; How to Recognize and Control Them. 11 +
414 pp., 606 figs. New York. Macmillan Co.
Sanderson, E. D. 1912. Insect Pests of Farm, Garden and Orchard. 12 + 684 pp., 513
figs. New York. John Wiley & Sons.
Bourcart, E. 1913. Insecticides, Fungicides and Weed Killers. Trans, by D. Grant.
35 + 431 pp. London. Scott, Greenwood & Son. New York. D. Van Nost-
rand Co.
Herrick, G. W. 1914. Insects Injurious to the Household and Annoying to Man. 17 +
470 pp., 152 figs., 8 pis. New York. - The Macmillan Co.*
Imms, A. D. 1914. The Scope and Aims of Applied Entomology. Parasitology, vol. 7,
pp. 69-87.*
Slingerland, M. V., and Crosby, C. R. 1914. Manual of Fruit Insects. 16 + 503 pp.,
396 figs. New York. The Macmillan Co.*
Hewitt, C. G. 1916. A Review of Applied Entomology in the British Empire. Ann. Ent.
Soc. Amer., vol. 9, pp. 1-34.
Osbom, H. 1916. Agricultural Entomology. Pp. 4 + 17-347, 252 figs. Philadelphia
and New York. Lea & Febiger.
Crosby, C. R., and Leonard, M. D. 1918. Manual of Vegetable-Garden Insects. 15 +
391 pp., 232 figs. New York. The Macmillan Co.*
Lochhead, W. 1919. Classbook of Economic Entomology. 14 -|- 436 pp., 257 figs.
_ Philadelphia. P. Blakiston's Son & Co.*
Femald, H. T. 1921. Applied Entomology. 14 + 386 pp., 388 figs. New York.
McGraw-Hill Book Co., Inc.
Sanderson, E. D., and Peairs, L. M. 1921. Insect Pests of Farm, Garden and Orchard.
Ed. 2. 6 + 707 pp., 604 figs. New York. John Wiley & Sons, Inc.
Most of the literature on the economic entomology of the United States is contained in
the following works: Reports U. S. Ent. Commission; Repts. Govt. Entomologists; Bulletins
U. S. Dept. Agric, Bur. Ent.; Bull. U. S. Dept. Agric; Journ. Agric. Research, U. S.
Dept. Agric; Insect Life; Reports and Bulletins by the several State Entomologists;
Bulletins of the various Experiment Stations; Journal of Economic Entomology.
INDEX
An asterisk * denotes an illustration.
Abbott, 461
Abdomen, 60; appendages of, *6i, *i32,
*i33; extremity, 62; modifications, 61;
segments, 60
Acacia, *2so
Accessory glands, *i24, 125
Acclimatization, 360
Acerentomon, *6
A chortiles,'^* 10
Acone, 98
Acridiidae (see Locustida).
Aculeata, 19
Adams, 339, 472, 475
Adaptations, of larvae, 145; of legs, 48, *5o;
of mandibles, *36; protective, 245
Adaptive coloration, 194; classification, 210;
evolution, 211
Adelung, von, 444
Adier, 439, 462
Adventitia, no
Adventitious resemblance, 197
Aedes, 255, 269
^geria, sexual coloration, 184
-Estivation, 366
Ageronia, 92
Aggressive resemblance, 210
Agrionidae, caudal gills, *ii9
Air, movement, 368; of soil, 350; of water,
383
Air-sacs, 117
Alary muscles, *io9
.\lbinism, 179
Aldrich, 384, 414, 426
Alexander, 460
Alimentary tract (see Digestive system) .
Allard, 445
Alluring coloration, 210
Alternation of generations, 216
Amans, 437, 455
Amber insects, 341, 345
Ametabola, 140
Ammophila, *3i7
Amnion, *i3i, 135
Amphidasis, 178
Amphigony, 358
Amphipyra, 304
Ampullaceum, *85
Anajapyx, *6, 21
Anal glands, 73, *io3
Anasa, *i38
Anderson, 269
Androconia, *7i, 72
Anemotropism, 305
Aner gates, 294
AngrcBcuni, 221
Anisota, *i52
Anisotropic, 78
Annelids, in relation to arthropods, 5, *8
Anomma, 293
Anopheles, 250, 251
Anophthalmus, 100
Anosia berenice, 337; plexippus, antenna of,
*32; dispersal, 325; eclosion, 152;
so-called mandibles, 40; mimicry, *20i,
207; pupa, *i47; pupation, 147; scale,
*7o; wing, *55
Anteclypeus, 29
Antecoxal piece, *47
Antennae, forms of, *32; functions, ^:^; sex-
ual differences, *3S
Antennal comb, *2 28, 229; neuromere, *43;
segment, 44; sensilla, 84, *85
Anthononius grandis, activity, 353; aestiva-
tion, 366; coloration, 378; develop-
ment, SS5, 359, 360; fecundity, 376;
food, 376; hibernation, 361; longevity,
377; rainfall on, 366; spread in U. S.,
418; winds on, 368
Anthrax, 269
Anthrenus, *6g
Antigeny, 34, *i84
Ant-plants, *23o
Ants, castes of, 289; color sense, 100; facets,
31; general account, 289; habits, 291;
harvesting ants, 297, 400; honey ants,
*294; hunting ants, 293; larvae, 290;
leaf-cutting, *295; nests, 290; photo-
tropism, 310; slavemaking, 293
48o
INDEX
Anurida, development of mouth parts,
*i32; germ band, *i32; habits, 170;
pigment, 177
Anus, *66, 105
Aorta, *io9
Apanteles, *2 73
Apatetic colors, 210
A pat lira, scales, 172; colors, 175
Aphididas, development, 359; galls of, * 2 14;
reproduction, 358
Aphidius, 273
Apis mellifera, antennal sensilla, *85; ce-
phalic glands, 107; comb, 282, *283;
control of sex, 286; determination of
caste, 286; foot, *5i; general account,
281; hair, *227; larvae, *284;legs, *228;
mandible, *36; mimicry, *202; modi-
fications in relation to flowers, *228;
mouth parts, *42; ocellus, *96; oviposi-
tor, *64; pupa, *284; reproductive sys-
tem, *i26; tongue, *86; wax, *74, 282
Apneustic, 117, 169
Apodemes, *48
Apodous larvae, 44, 5 1
Apophyses, *48
A poms, 319
Appendages, development of, *i3i
Apple, insects of, 212, 410
Aptera, 7
Apterygota, 9
Aquatic insects, adaptations of, 165; condi-
tions of existence, 382; food, 165,* 386;
locomotion, 166; origin, 171; respira-
tion, 168; systematic position, 165
Arachnida, *2
Arctic realm, 331
Arista, *32
Aristida, 297
Arixeniidae, 10
Arms, J. M., 21, 431, 432, 454
Army worm, 339
Arthropoda, characters of, *i; classes, 2;
interrelationships, 4; naturalness of
phylum, 7; phylogeny, *8
Asclepias, 221, *222, *223
Asecodes, 274
Ashmead, 327
Aspidiotus perniciosits, spread of, 418;
\vinter-killing of, 363
Assembling, 90
Associations, 393, 394
Ast, 446
Atelnra, *300
Atemeles, *299
Atmosphere, 351; composition of, 367;
movement, 368^ temperature, 352
Atta, 293, *295
Attactis, 27
Auditory hairs, 94; organs, 94, *9S
Aughey, on insectivorous birds, 243, 463
Auricle, *228, 229
Austen, 465
Australian realm, 332
Austral region, 332
Autecology, 348
AiUomeris, 73
Ayers, 61, 452
Bachmetjew, 364
Back, E. A., 429
Backswimmers (see Notonecta).
Baldwin, 469
Ball, E. D., 426
Ballowitz, 450
Banks, 430, 434
Barber, 384, 456
Barriers, 324
Barrows, 303, 470
Basement membrane, *67, 69, *io5
Basiconicum, 84, *85
Basidium, *2i8
Basilarchia, mimicry, *2oi, 207; protective
resemblance, 196
Bates, on mimicry, 202, 459, 470, 471
Batesian mimicry, 203
Bateson, 458
Bauer, 442-
Baumberger, 354, 361, 373, 374, 475, 476
Beal, 240, 463
Bean weevil (see Bruchus).
Beddard, 457, 460, 472
Bees, color sense of, 100; hairs, *68
Beetles, sounds of, 91
Behavior of insects, 302
Bellesme, de, 446
Belostoma, digestive system of, ^105; pre-
daceous, 166, 233
Belt, on leaf-cutting ants, 295, 471
Bembidion, 303, 349
Benacus, *i5; caecum, 105; mouth parts,
*39; predaceous, 166
Beneden, van, 466
Beneficial insects, 41 1
Benton, oh honey bee, 286, 466
INDEX
481
Berlese, 160, 431, 433
Bernard, 432
Bertkau, 126
Bethe, 292, 469
Bethune, 429
Betten, 456
Binet, 442
Biotic conditions, 379, 387
Birches, insects of, 212
Bird, H., 349
Birds, insectivorous, 239; regulating insect
oscillations, 243
Bishopp, 352, 365, 475
Bittacomorpha, *i20, 169
Biltactis, *i6, *49
Bitter rot, 219
Black-flies, 233
Blackiston, 460
Blanc, 436, 447
Blanchard, 464
Blandford, 464
Blastoderm, *i3o
Blastophaga, 428
Blatchley, 426
Blalla, muscles of, *77; respiration, *i2i
Blattidje, 10
Blind insects, 2,3
Blissus leiicopterusy distribution of, 339;
drought on, 366; incubation, 359;
losses through, 410; rainfall on, 367
Blochmann, 452
Blood, corpuscles, *iio; course of, no,
*iii; function, in; gills, 119
Bluebird, food of, 241
Blunck, 453
Boas, 455
Bobretzky, 452
Boll weevil (see Anlhonomus).
Boll worm (see Chloridea).
Bolton, 430
Bombiis, antenna of, *32; general account,
287; larva, *i42; mimicry, *2io; respi-
ration, *i2i; taste cup, *88
Bombyx mori, Malpighian tubes of, *io8;
mid intestine, *io5; cenocytes, *n4;
silk glands, *76
Bordas, 441, 447
Boreal region, 332
Borgert, 441
Borner, 433, 434
Bot flies, 234
Bourcart, 477
31
Bouvier, 433, 470
Boyce, 465
Brachiniis, 73
Brachj'pterism, 397
Braconidas, 273
Brain, 80, *82; functions of, 82
Branchial respiration, 169
Brandt, 451
Brauer, on classification, 7; types of larvae,
142)432, 453
Br aula. 272
Braun, 464, 465
Breed, on phagocytosis, 160
Breithaupt, 436
Bridges, 461
Britton, 425
Brongniart, on Carboniferous insects, 341,
344,.473
Brown-tail moth (see Euproctis).
Bruce, 263, 264, 465
Bruchophagiis, *I39
Bruchus, metabolism, 364, 370
Brues, 269, 359, 366, 372, 374, 434, 465, 467,
476
Bruner, 426
Brunner von Wattenwyl, 458
Bruntz, 448
Buckingham, 470
Bugnion, 162, 454
Bumblebees, general account, 287
Bureau of Entomology, 428
Burge, lis
Burger, 370
Burgess, A. F., 368, 429
Burgess, E., 436
Burmeister, 431, 432
Bursa copulatrix, 125
Busck, 139
Biithus, *2
Butler, 459
Biitschli, 442, 450, 451, 452
Butterflies, eclosion of, 152, *i53; fossil,
*346
Cabbage butterfly (see Pier is rapa).
Caeca, gastric, *io2, *io3, 104
Cacilius, *io6
Cascum, *io4, *io5
Caesar, 445
Cajal, 449
Calkings, 465
CaUiphora, compound eyes of, *97, *98
482
INDEX
Callosamia, antennae, 2>y': assembling, 90;
cocoon, 356; sexual coloration, *i85
Caloptenus, olfactory organ of, *88; tym-
panal organ, *95
Calopteryx, development of, *i34; sexual
coloration, 185
Calvert, 465
Cameron, 475
Campodea, 6, *g, 21, 60, *i42
Candeze, 440
Canker worms, as food of birds, 243
Cannon, 307
Canthon, *5o
Capitate, *32
Carabids, anal glands of, 73, *io3; food of,
233; predaceous, 271
Carabidoid larva, *i57
Carahus, alimentary tract of, *io3
Carboniferous insects, 341, 342
Cardiac valve, *ioi, 102, *io4
Cardo, *37
Carle t, 439
Carpenter, F. W., 469
Carpenter, G. H., 5, 7, 43I) 433, 455, 45^,
461, 472
Carpocapsa pomonclla, development, 356,
360; hibernation, 361; incubation, 358;
temperature on, 356; winter-killing of,
362
Carriere, 444, 452
Carrion insects, 236
Carroll, 253, 255, 465
Cams, 430
Casteel, 229, 463
Catbird, foot of, 240
Caterpillar, 137; pupation of, 147, *i49
Catocala, protective resemblance, *i9s;
scent tufts, 49
Caiogenus, antenna of, *32
Caudal gills, 170
Caudell, 434, 435
Cecidomyiidie (see Itonidida).
Cecropia adettopus, 230, *23i, *232
Cecropia moth (see Samia).
Centipede, *5
Centrolecithal, *i30
Cerambyx, facets of, 31; ovipositor, *63
Ceralina, 277
Ceratomegilla, 336
Cerceris, 319
Cerci, *g, 62, *6s, *6s
Cercopoda, 62
Ceroplaslcs, 75
Cerura, 74
Cervical sclerites. 29
Chadwick, 463
Chajticum, 84, *85
Chalcididae, 27, 273
Chandler, 465
Chapman, 453
Chelostoma, *68
Chemotropism, 302
Cheshire, 42, 64, 229, 283
Child, 444
Chilopoda, 3, *5
Chinch bug (see Blissiis).
Chionaspis, 141
Chironomus, nervous system, *82; pupal
eggs, 128
Chitin, 66
Chittenden, 429, 474, 477
Chloridea obsoleta, development, 359; rain-
fall on, 366
Chlorophyll, as a pigment, 175
Cholera, 268
Cholodkovsky, 432, 447, 452
Chordotonal organs, *95
Chorion, *i29, 141
Christophers, 465
Christy, 464
Chro mosomes, 1 2 9
Chrysalis, 137
Chrysobothris, integument of, *67
Chrysomelidae, silk glands of, 77
Chrysopa, *i6; cocoon of, *i48; laying eggs,
*i4o; mandibles, *36; predaceous, 270;
silk glands, 77
Chun, 440
Cicada, metamorphosis of, *i39; molts, 145;
sound, 91
Cicindela, leg of, *5o; mandible, *s6; pre-
daceous, 271; variation in coloration,
183, 189, *I92
Cicindelidae, ecological succession of, 407;
eggs, 350, 351
Cimbex, repellent glands, 73
Circular muscles, *io5, 106
Circulation, *iii
Circulatory system, 109
Cirphis unipuncta, 339
Claassen, 476
Claspers, *65, *66
Claus, 432
Clavate, *32
INDEX
483
Claypole, 453
Clements, 474
Climatal coloration, 179
Clisodon, 225
Cloaca, 62
Clover, insects of, 212, 410; pollination of,
225
Clypeus, 28, *4o
Clylra, embryology of, *i30, *i3i, *i3S,
*i36
Cnemidotus, 118
Coarctate pupa, 147
Coblentz, 116, 449
Coccinella, distribution of, 336
Coccinellidc-E, predaceous, 271; silkglands, 77
Cochineal, 413
Cockerell, 347, 426
Cockroach, cephalic ganglia of, *82; fossil,
*343j 345; mouth parts, *35; muscles,
*53> *77; respiration, *i2i; salivafy
gland, *io7; spermatozoon, *i25
Cocoon, *i48, *isi
Codling moth (see Carpocapsa).
Cceloconicum, 84, *85
Ccelom sacs, "135
Coleoptera, 16, *i5, 24
Colias, albinism of, 180; color sense, 100;
sexual coloration, *i84
Collembola, alimentary tract of, *ioi; de-
fined, 9; furcula, 62; primitive condi-
tion, 21; ventral tube, 62
Colletes, hairs of, *68
Colon, *io2, 105
Colopha, gall of, *2i4
Coloradia, 414
Color, effects of food on, 176; sources of, 172
Colorado potato beetle (see Leptinotarsa).
Coloration, adaptive, 194, 210; climatal,
179; development of, 187; effects of
moisture and temperature on, 178;
seasonal, 180; sexual, 184; variation in,
188; warning, 199
Color patterns, development of, 187; ori-
gin, 186
Colors, combination, 175; pigmental, 174;
structural, 172
Color sense, 100
Commissures, 80, *82
Communities, 393; classification of, 389,
393; distribution of, 389; examples of,
394; grasshopper, 394; stream, 397; in
New Mexico, 399
Complete metamorphosis, 137
Compound eyes, *25; origin, 100; physiol-
ogy) 98; structure, *97, *98
Comstock, A. B., 128, 290
Comstock, J. H., 56, 424, 427, 431, 432, 433,
434, 435, 436, 438, 455, 45^
Comte, 267
Cone cells, 97, *98
Conidia, *2i8
Conidiophores, *2i8
Connold, 462
Conradi, 426
Conseil, 267
Consocies, 393
Cook, A. J., 426
Cook, M. T., 462
Cooke, 462
Cooley, 426
Cooties (see Pediculus).
Cope, on segmentation, 27
Copidosoma, 273, 412
Copris, spermatozoon of, *i25
Coprophaga, 373
Coquillett, 424
Corbiculum, *228
Cordley, 426
Cordyceps, *2i7
Corethra, chordotonal organs of, *95; imag-
inal buds, *i6i
Corn borer (see Pyrausta).
Corn ear worm (see Chloridea).
Corn insects, 212, 410
Cornea, *97, *98
Corrodentia, *i2
Corydaloides, 344
Cosens, 215, 463
Costa, *54
Coste, 457
Cotton boll weevil (see Anthonomus) .
Cotton boll worm (see Chloridea).
Cotton worm, 410
Cowan, 462
Coxa, 48
Craig, 465
Craighead, 476
Crampton, 21, 23, 25, 434, 435, 437, 438,. 440
Crawley, 467
Cremaster, 147
Cremastogaster, 291
Cricket, stridulation of, 93
Crioceris, 338
Crop, *i02, *io3
484
Crosby, 424, 477
Crustacea, 2
Cryptorhynchus, 338
Crystalline cone, 97, *98
Ctenocephalus, *20
Cubitus, *54
Cucurbit wilt, 219
Cuenot, 441, 447, 448
Ciilex, antennae of, *34; characteristics, 251;
filariasis transmitted by, 265; hiberna-
tion, 310; larva, *i68; mouth parts,
*4i; respiration, 169; tropisms, 310
Cutaneous respiration, 169
Cuticula, 66, *67, *68
Cuticular colors, 1 74
Cyaniris pseudargiolus, coloration of, 178;
geographical varieties, 328; melanism,
180; polymorphism, *i8i; sexual color-
ation, 184
Cybister, leg of, *i67; locomotion, 167, 168
Cychrits, 91
Cyllene, metamorphosis of, *i37
Cynipidse, abdomen of, 61; galls, *2i3,
*2i4; parthenogenesis, 127, 216
Cyrtophyllus, stridulation of, 93
Dahl, 437, 440, 442
Darkness, as affecting pigmentation, 177
Darts, *64
Darwin, 317, 412, 461, 462, 470
Dasyneura, egg of, *i39, 140; ovipositor, *63
Davenport, 308, 352, 353, 360, 364, 469, 474
Davis, J. J., 426
Davis, K. C, 456
Dean, 425
Dearborn, on insectivorous birds, 242, 243,
245, 464
Deegener, 441, 442, 443, 445, 447, 448, 450,
45i> 455
Demoll, 437, 445, 446
Demoor, 437
Denny, 66, 78, 431, 435, 442
Dermaptera, 10
Dermestidae, 236
Deutocerebrum, 80, 135
Deutoplasm, *i29
Development, 129
Development, threshold of, 355
Developmental zero, 355
Devonian insects, 340, 341
Dewar, 461
Dewitz, 437, 439, 448, 454
Diabrotica, distribution of, 337
Diacrisia, cocoon of, 148
Diapheromera, 195, 359
Diastole, in
Dibrachys, 274
Dichoptic, *32
Dickel, 467
Dictyoneiira, 344
Dietrich, 445
Digestive system, loi; of beetle, *ioy,
Belosloma, *io5; Collembola, *ioi;
grasshopper, *io2; histology, *io5;
106; moth, *io4; Myrmeleon, *io3
Digoneutic, 182
Dimmock, on assembling, 91; on mouth
parts of mosquito, *4i; 436, 440, 457,
463
Dimorphism, 180
Dinar da, *2gg
Dineutus, antenna of, *32; eyes, *30
Diplopoda, *3
Diptera, 19, *2o; eyes of, *3i; halteres, loi;
mouth parts, *4i; origin, 25; sounds,
91; spiracles, 60
Direct metamorphosis, 138
Directing tube, 76
Diseases, their transmission by insects, 218,
248
Dispersal, 322; centers of, 339; means of,
323; in North America, 335
Dissosteira, protective resemblance of, 196;
stridulation, 92
Distant, 471
Distribution, former highways of, 325; geo-
graphical, 322; geological, 340; tem-
perature on, 362
Diving beetles (see DytiscidcB).
Dixey, 208, 457, 458, 460
Doane, 465
Dogiel, 447
Dolbear, on stridulation, 93
Dolichopodidae, 49
Dolley, 470
Donacia, 79, 165, 169
Doncaster, 451
Donisthorpe, 467
Dorfmeister, 457
Dorsal vessel, *io9, *iio
Doten, 376, 426, 474
Dove, 352, 365, 475
Dozier, 476
Drift, insect, 1 70
INDEX
485
Drone, *282
Drosera, 216
Drosophila, chemotropism of, 303; egg,
♦139; food, 373, 376; humidity on, 365;
melanism, 180; phototropism, 310, 311
Drought, 366
Dubois, 448
Ductus ejaculatorius, *i24
Dufour, 449, 455
Durham, 464
Diirken, 438
Dyar, on molts, 145
Dynastes hercules, 27; tityiis, distribution of,
337
Dysentery, 268
Dytiscidae, 166, 167
Dytiscus, caecum of, 105; leg of, *5o; pre-
daceous, 233; respiration, 169
Dzierzon's theory, 286
Ecdysis, 140, 144
Ecilon, *295; eyes of, 31; habits, 233, 290,293
Eckstein, 462
Eclosion, 152
Ecology, 348
Economic entomologist, 420
Ectoderm, 130, *i3i
Edwards, on /. ajax, 182; on P. tharos, 182
Effective temperatures, 355
Egg-guide, *67
Egg-nucleus, *i29
Eggs, form of, *i39; number, 141; size, 140
Eimer, 468
Ejaculatory duct, *i24
Elaplirus, stridulation of, 91
Electricity, 368
Eleodinae, 372
Ellema, protective resemblance of, 196
Elm, insects of, 212
Elm leaf beetle (see GaleruccUa).
Eltringham, 446, 461
Elwes, 471
Elwyn, 365, 475
Ely, 476
Elytra, 53
Enihia, 12
Embioptera, ix
Embryology, 129
Emery, 448, 467
Emcsa, 322
Empis, nervous system of, *82
Empodium, 48
Emptisa, *2i8
Enderlein, 433
Endoskeleton, 46, *48
Engelmann, 430
Enteman, 289, 321, 459, 467, 469
Entoderm, 130, 135, *i36
Entomophagous, 373
Entomophthoracea;, 217, *2i8
Environment, 387, 389
Ephemerida, *i3, 14; abdominal segments
of, 60; eyes, 31; origin, 23
Ephydra, 383, 414
£/)/f aw/a, hypermetamorphosis of, 156, *i57
Epicranium, 28
Epigamic colors, 211
Epimeron, *45, *47
Epipharynx, 35
Episternum, *45, *47
Epitheca, dorsal vessel of, *iio
Equilibrium, 382
Erebus agrippina, 27; odora, 323, 337
Ergatoid, 290
Eriocepliala, mouth parts of, 40
Eristalis, mimicry by, *202; respiration, 169
Eruciform larvae, 24, *i43, 160
Erynnis manitoba, distribution of, *332
Escherich, 439, 451
Essig, 425
Ethiopian realm, 331
Etiolin, 193
Etoblattina, 343
Eucone, 98
Eitdamus proteus, distribution of, *332
Eiigercon, *344
Euphoria, mouth parts of, 36, *2 2 7
Euplexoptera (see Dermaptera).
Euplcea, colors of, 175
Euproctis chrysorrhoea, phototropism of,
309; spread, 417; winter-killing of, 362
European corn borer (see Pyrausta).
Euschistus, antenna of, *32
Eutermes, 281
Eiithrips, *i4
Evaporation, 369; adaptations to, 372; on
eclosion, 372; gradients, 371; on hatch-
ing, 371; on life cycle, 371; on metabo-
lism, 369; reactions to, 370
Everes, androconium of, *7i
Ewing, 4, 359, 435
Excrements, 105
Exner, on compound eyes, 98, 444, 468
Expiration, 123
486
INDEX
Exuviae, 144
Eyes, compound, *30, *97; kinds of, *3o;
sexual differences in, *3i; simple, *30,
*3i
Fabre, J. H., 316, 466, 468
Fabre, J. L., 446
Facets, *30
Fat-body, distribution of, 112, *ii3; func-
tions, 112; structure, 112, *ii3, *ii4
Fat-cells, 112, *ii3
Faunae of islands, 326
Faunal realms, 328, *329
Faussek, 447
Felt, E. P., 423, 451, 463
Female genitalia, 62, *6s
Femur, *47, 48, *49
Fenard, 451
Fenestrate membrane, 97, *98
Feniseca, 271
Fernald, C. H., 213, 423, 425, 426
Fernald, H. T., 426, 432, 477
Fertilization, 129
Fidonia, antennal sensilla, *85
Fielde, 290, 292, 307, 466, 467, 469
Fielding-Ould, 464
Filariasis, 265
Filiform, *32
Filippi's glands, *76
Finlay, 253, 464
Finn, on mimicry, 206; on warning colora-
tion, 199; 460, 461
Fire blight, 218
Fire-flies, 115, 116
Fischer, 45 8
Fishes, insectivorous, 237
Fitch, 423
Flagellum, *32
Fleas, *2o, 234
Fletcher, 429
Flight, mechanics of, 57
Flint, W. P., 425
Flogel, 442
Fluted scale, 428
Follicles, 124, *i27
Folsom, 433, 436, 447
Food, its effects on color, 176, 378; on fecun-
dity, 376; on growth, 375; habits, 373;
on hibernation, 378; on longevity, 377;
on oviposition, 376; plants, 373; rela-
tions, 378; on reproduction, 376; selec-
tion, 374; on sex-determination, 376
Food reservoir, 102, *io4
Forbes, H. O., 471
Forbes, S. A., on corn root louse, 298; on
economic entomologist, 420; food of
Carabidae, 271; insectivorous birds,
239; insectivorous fishes, 237; insect
oscillations, 243; 424, 462, 463,. 464, 466
Forbush, 213, 423
Fore intestine, *ioi, *io2
Forel, on ants, 291; on taste, 85; 440, 443,
444, 445, 467, 469
Forficulidae, 10
Formations, 393, 394
Formative cells, 69, *7i
Formica, exsectoides, mounds of, 2gi;fusca,
289, 293, 294; pratcnsis, eyes of, 33;
sangiiinea, 294
Fossil insects, localities for, 340
Fossilization, 340
Free pupa, 146
French, G. H., 424
Frenulum, 54
Frenzel, 446, 447
Friese, 459
Front, *28, *29
Frontal ganglion, 81, *82
FuUer, 467
Fundament, 131
Fungi of insects, *2i 7, *2 1 8
Furcae, 46, *48
Furcula, 62
Futaki, 266
Gadeau de Kerville, 448
Gad flies, 233
Galapagos Islands, Orthoptera of, 326
Galea, *35, 37, *38
Galerita, anal glands of, 73; antenna, *32;
sternites, *47
Galerucella luleola, 419
Galls, *2i3, *2i4
Ganglia, cephalic, *43, 80, *82; functions of,
82
Ganglion, structure of, 81, *83; suboesopha-
geal, *8i, *82; supraoesophageal, 80,
*82
Ganglion cells, 81, *83
Ganin, on Platygaster, *is8, 454
Garman, 426, 456
Gastric cffica, *io2, *io3, *I04
Gastro pacha, larval coloration, 177; stinging
hair, *72
INDEX
487
Gastraphilus, 235
Gastrulation, *i3o
Gee, 470
Gehuchten, van, on digestion, 104; 442, 447
Gens, *29
Geniculate, *32
Genitalia, 62; of female, 62; grasshopper,
*67; male, 64; moth, *66
Geographical, distribution, t,22; varieties,
328
Geological distribution, 340
Geometridse, legs of larva% 5 r
Geotropism, 306
Gerephemera, 342
Germ band, *i3o; types of, 133
Germ cells, 129
Germinal vesicle, 129
Gerould, 180, 459, 461
Gerris, *i66; locomotion of, 168; thigmo-
tropism, 304
Gerstacker, 449
Gibson, A., 429
Gibson, W. H., 462
Gill, T., 471
Gillette, 426
Gills, *ii8, *ii9, 169
Gilson, 447, 450, 456
Gipsy moth (see Porthetria).
Girault, on numbers of eggs, 141
Gizzard, 102, *io3
Glaciation, its efifects on distribution, 325
Glands. 72: accessory, *i24, *i26; alluring,
74; repellent, 73; salivary, *io6, *io7;
silk, 75, *76, wax, 74
Glandular hairs, *72, *73
Glaser, 114, 449
Gleason, 474
Glenn, 356
Glossa, *35, 7,t, *^2
Glossina, 262, *263
Glover, 427
Golgi, on malaria, 248
Goliathus, endoskeleton of, *48
Gonapophyses, *63, *64
Gongylus, 210
Gonin, 454
Goossens, 439, 440
Gorgas, 256, 465
Gortner, 174, 459
Goss, 473
Gossard, 425, 426
Gould, 457
Graber, on chordotonal organ, *95; hal teres,
loi; hearing, 94; 431, 437, 439, 443,
447, 452, 468
Graham, 269
Grasshopper, adaptations, 397; alimentary
tract, *io2; communities, 394; geni-
talia, *67; hearing, *94
Grassi, on Termes, 279; 432, 464, 466
Green bug (see T 0x0 pier a).
Gregory, 376
Gregson, 176
Grenacher, on compound eye, 98, 100, 443
Grobben, 432
Gross, 451
Grossbeck, 384, 456
Growth, 144
Grub, 137
Griinberg, 451, 465
Gryllidse, 10
Grylloblattidae, 10
Gryllotalpa, leg of, *5o; maternal care, 76
Gryllus, sense hairs, *9o; stridulation, 92
Gula, 29, 37
Giinther, 445
Guy6not, 376
Gynandromorphism, 127, *i28
Gyrinidae, eyes of, *30
Gyrinus, locomotion of, 168; respiration,
169; tracheal gills, *ii8
Haase, 432, 439, 449, 460
Hsemolymph, no
Hagen, 279, 430, 455, 457
Hairs, development of, *68, 69; functions,
69; histology, *6g; modifications, *68;
pollen-gathering, *6o, *227; protective,
245; tenent, *72
Halisidota, distribution of, 336
Halobaies, 170
Halteres, 53, loi
Hamilton, on holarctic beetles, 331, 471
Hammar, 358, 360
Hammond, A. R., 454
Hammond, J. H., Jr., 312
Hamuli, 54
Handlirsch, 8, 347, 433, 434, 435, 474
Hansen, 432, 433, 436
Harmolita, 273
Harned, 426
Harpactophagous, 373
Har pains, labium of, *38; maxilla, *38
Harris, 423, 476
INDEX
Hart, 456, 474
Hartman, 469
Harvey, 425
Hatching, 141
Hatschek, 452
Hauser, on smell, 87, 443
Haushaltef, 268
Haviland, on termites, 281
Hawaii, beetles of, 326; Hymenoptera, 327
Hayward, on stridulation, 93
Head, 28; segmentation of, *43
Headlee, 356, 359, 364, 367, 370, 372, 425,
475-376
Hearing, 94
Heart, *io9, *iio, *iii
Heath, on Termopsis, 278, 467
Heer, on fossil insects, 341, 473
Heider, 452, 454
Heilprin, 472
Heim^ 462
Heinemann, 448
Heliconiidae, mimicry, 202
HcUophila (see Cirphis).
Heliotropism, 306; machine to illustrate,
311
Helm, 446
Hemelytra, 53
Hemerocampa, parasites of, 274
Hemimeridae, 10
Hemimerus, *ii; hypopharynx of, *38
Hemiptera, 16; mouth parts, *39; odors, 73;
origin, 23
Henking, 450, 452
Henneguy, 431
Hennings, 370
Henshaw, 430
Heptagenia, hypopharynx of, *;,&
Hermaphroditism, 125
Herms, 425, 465, 470, 474
Herrick, 424, 426, 477
Hesse, 445
Hessian fly (see Mayetiola).
Hctarius, 300
Heterocera, 18
Heterogeny, 127
Heterogony, 358
Heterometabola, 138
Heterophaga, 19
Heteroptera, *i6; spiracles of, 60
Hewitt, 375, 429, 436, 477
Hexagenia, *i^, 14; male genitalia, *65;
tracheal gills, *ii8
Hexapoda, defined, 4
Heymons, 139, 433, 439, 451, 453
Hibernation, 361
Hicks, on olfactory pits, 88
Hickson, 444
Higgins, 456
Hildebrand, 384
Hilton, 441
Hind intestine, *io2, *io4
Hinds, 354, 355, 359, 360, 361, 366, 367, 377,
378, 426
Histogenesis, 160
Histolysis, 160
Hochreuther, 445
Hodgkiss, 424
Hoffbauer, 438
Holarctic realm, 331
Holcaspis, galls of, *2i3, *2i4
Holmes, 69, 470
Holmgren, 436, 443, 450, 451, 467
Holometabola, 137
Holopneustic, 117, 168
Holoptic, *32
Homoptera, 16
Honey, 285, 413
Honey ants, *294
Honey bee (see Apis mellifera).
Hopkins, A. D., 426, 429
Hopkins, F. G., on pigments, 175, 458
Hoplia, sexual coloration of, 185
Horn, on Cicindela, 189
Houghton, 426
House fl}^ (see Miisca).
Houser, 425
Howard, 274, 338, 423, 428, 429, 431, 464,
465, 466, 472, 477
Howes, 470
Hubbard, on parasitism. 274
Huber, on wax, 282
Hudson, 471
Humboldt ia, 232
Hunter, S. J., 356, 426, 431
Hunter, W. D., 354, 355, 359, 360, 361, 366,
367, 368, 375, 376, 378, 428, 429
Huxlej^, 450
Hyaloplasm, 78
Hyatt and Arms, 21, 160, 431, 432, 454
Hybernia, 176
Hydno phylum, *232
Hydrophilus, *i5, *i66; antennae, 33; leg,
■•167; locomotion, 166; male genitalia,
*65; respiration, 169
489
Hydrotropism, 303
Hydrous, tergites of, *46
Hylastinus, 338
Hylobius, glandular hairs of, *72
Hymenoptera, defined, 18; cephalic glands,
107; eyes of sexes, *32; internal meta-
morphosis, 162; mouth parts, *42;
ocelli, 31; origin, 25; sounds, 91; wing,
*56
Hypatus, 364
Hypera, 338
Hypermetamorphosis, 156
Hyperparasitism, 274
Hyphze, 217
Hyphantria, 246
Ilypoderma, lar\'a of, *i42; lincala, habits
of, 235; losses through, 411
Hj-podermal colors, 174
HjTJodermis, *67, *68
Hypognathous, 11
Hypopharynx, *ss, 37, *38, *4i
I eery a, 428
Ichneumonid^, *2 72
Ileum, *io5
Imaginal buds, *i6r, *i62
Imago, 137
Imms, 477
Incomplete metamorphosis, 138
Incubation, 358
Indirect metamorphosis, 137
Ingenitzky, 451
Injurious insects, 410; introduction of, 416
Ino, antennal sensilla of, *85
Inquilines, 215, 281
Insecta, defined, 4
Insectivorous birds, 239; fishes, 237; plants,
216; vertebrates, 236
Inspiration, 123
Instar, 140
Instinct, 313; apparent rationality of, 314;
basis of, 313; flexibility, 316; inflexi-
bility, 315; modifications, 315; origin,
317; stimuli, 314; and tropisms, 318
Integument, 65
Intelligence, 318
Interactions of organisms, 379
Intercalary, appendages, *i32; neuromere,
*43; segment, 44
Interglacial beetles, 346
Interrelations, of insects, 270; of orders, 20
Intima, *76, 106, *i2i
Iphiclides ajax, polymorphism of, 181
Iridescence, 172
Iris pigment, *96, *97
Iris versicolor, *2 20, *2 2i
Irritants, 246
Isaria, 217
Isia, cocoon of, 148; hairs, 69, 146; hiberna-
tion, 361; molts, 145
Island fauna?, 326
Isolation, 328
Isoptera, 11
Isosoma (see HarmoUta).
Isotropic, 78
Ithomiinae, mimicry, 202, 203
Itonididse, galls of, 214; paedogenesis, 128
Jackson, C. F., 431
Jackson, T. W., 465
Jacobi, 461, 472
James, W., 468
Janet, on Atelura, *3oo; on muscles, *78;
436, 4395 440, 442, 466, 467
Japan, 415
Japanese beetle (see PopiUia).
Japyx, 9, 22; spiracles of, 60
Jennings, 469
Johannsen, 456, 465
Johnson, R. H., 459
Johnson, W. G., 426, 477
Jordan, 436
Jorschke, 445
Judd, on food of bluebird, 242; mimicry,
208; protective adaptations, 245; pro-
tective resemblance, 198; warning col-
oration, 199; 460, 463, 464
Jugum, 54
Jurassic insects, 341, 345
Kala-azar, 269
Kallima, protective resemblance of, *i94
Kanthack, 464
Kapzov, 441
Kathariner, 469
Katydid, stridulation of, 93
Kellogg, on Mallophaga, 233; mouth parts,
40; phototropism, 310; pilifers, */\o;
scales, 70, 172; swarming, 286; 431,
43S> 436, 458
Kenyon, 432, 443
Kidney tubes, *io8
Kielich, 442
Kilborne, 269
490
INDEX
Kingsley, on Arthropoda, 7
Kirby, 431, 432
Kirkland, 463
Klemensiewicz, 440
Kluge, 451
Knuppel, 447
Koch, 250
Kochi, 436
Koestler, 442
Kolbe, 431
Kolliker, 442
Korotneff, 452
Korschelt, 450, 452, 453, 454
Kowalevsky, 447, 448, 451, 454
Kraepelin, 436
Krancher, 449
Krause's membrane, *78
Krogh, on temperature- velocity, 357; pupal
development, 359
Krukenberg, 67
Kulagih, 41, 436, 453, 454
Labellum, *4i, *42
Labial, neuromere, *43, 81, 135; segment, 44
Labium, 29, *-s5 37, *38, *39*4i
Labrum, *29, *35, *39
Lac, 75, 413
Lachnosterna, antenna of, *32; cocoon, 148;
larva, *i42
Lacinia, *35, 37, *38
Lagoa, legs of, 51; stinging hairs, *73
Lamarck, on instinct, 317
Lameere, 455
Lamellate, *32
Landois, 449
Lang, 435
Langley, on luminosity, 115
Lankester, 433
Larvae, 137; adaptations of, 145; legs, 50;
nutrition, 145; parasitic, 275; types of,
*I42
Lasiiis, age of, 289; nest, 291; parthenogene-
sis, 128
Lathrop, 470
Laveran, on malaria, 248, 465
Laverania, 248, *249
Leachia, eyes of, *3o
Leaping, 52
LeBaron, 424
LeConte, 470
Lee, on halteres, loi; 444
Legs, adaptations of, 48, *5o; larval, 50;
Legs, mechanics, *52; muscles, *S5', seg-
ments, *49
Lendenfeld, von, 437, 441
Leng, 456
Lens, *96
Leonard, 477
Leopard moth (see Zeiizera).
Lepidocyrtus, scales of, 70
Lepidoptera, defined, 18; internal metamor-
phosis, *i62; molts, 145; mouth parts,
*4o; origin, 25; reproductive organs,
*i24, *i 26; silk glands, * 76; spiracles, 60
Lepidotic acid, 176
Lepisma, *g, 21, *i42; spiracles of, 60
Leptinotarsa decemlineata, aestivation, 366;
color pattern, 175, 186, *i9i; distribu-
tion, 336, 338; dorsal wall, *i35; ento-
derm, *i36; folding of wing, *57;
hibernation, 365; spread, 338; varia-
tion in coloration, *i9i
Leptocoris, 339
Leptosphceria, 219
Leptospira, 255
Lerema, ocellus of,- 31
Leuckart, 451
Leucocytes, *iio, 114, 160
Leydig, 442, 446, 450
Libellula, *i4, *i42
Lice, biting, *i2, 223; sucking, *i5, 234
Life zones, 332, *sss
Light, 351; on activity, 352; growth, 352;
pigmients, 177
Ligula, *38 '
Limacodes, scale of, *6g
Una, color changes of, 190; distribution,
336; germ band, *i3i; glands, 74
Linden, von, 458, 459
Lingua, ^38
Link, 445
Linnaeus, on orders of insects, 7
Lintner, 423, 476
Lithomantis, *2,AZ
Livingston, 369, 389, 391, 476
Lloyd, 456
Locality studies, 319
Lochhead, 477
Locustidae, 10; molts of, 144
Locy, 446
Lodeman, 477
Lodge, 470
Loeb, 302, 304, 305, 306, 308, 309, 311, 373,
468, 469, 470, 476
491
Lomechusa, *2<)g
Longitudinal muscles, *io5, io6
Lord, 268
Lorum, *42
Losses through insects, 410
Lovell, 445
Low, on malaria, 250
Lowe, 424
Lowne, 435, 443, 444, 450
Lubbock, on ants, 289, 290, 292, 294, 297,
298, 307; larval characters, 146; mus-
cles, 78; vision, 99; 432, 441, 443, 444,
454, 462
Lucanus, cocoon of, 148; dorsal vessel, *io9;
spiracles, *i2o
Lucilia, *3o6
Lugger, 425
Liihe, 465
Luks, 442
Luminosity, 114
Lund, 448
Lutz, 383, 385, 432, 456
Lycana, facets of, 31
Lycaenid larvae, alluring gland of, 74
Lyais, mimicked, 206, 207
Lyon, 304
Lyonet, on muscles, 78; 435, 441
MacGillivray, 456
Machilis, 9, 21; abdominal appendages, *6i;
nervous system, *8i; scales, *69;
spiracles, 60
Macloskie, 449, 455
Macrosiphum pisi, interactions of, 380
Madeira Islands, beetles of, 326
Maggot, 137
Malacopoda (see Onychophora).
Malacosoma, eggs, 141
Malaria, 248, ^249
Male genitalia, 64, *65, *66
Mallock, A., 444
Mallock, H. R. A., 438
Mallophaga, *i2, 233
Malpighian tubes, *io8
Mammen, 450
Mandibles, *35; adaptations of, *2>^; Culex,
*4i; Lepidoptera, *4o
Mandibular, neuromere, *43, 81, 135; seg-
ment, 44
Mandibulate mouth parts, *35; orders, 34
Mandus, 461
Mann, 141
Manomcra, *iq^
Manson, on filariasis, 265; malaria, 250; 465
Mantida;, 10, 270
Mantis pa, 24; metamorphosis of, *i43
Maples, insects of, 212
Marchal, 136, 453
Marey, on wing vibration, 58; 437, 438
Ma'T gar opus, 269
Marine insects, 170
Mark, E. L., 444
Marlatt, 428, 429
Marshall, on adaptive coloration, 206, 207,
460, 461
Martin, 438
Mast, 470
Maternal provision, 276
Maturation, 129
Maxillae, 37, *38
Maxillary, neuromere, *43, 81, 135; seg-
ment, 44
Maxillulae, 36
Mayer, A. G., on color pattern, 188; Papilio,
179; scales, 71 ; 441, 458, 460
Mayer, A. M., on Culex, 94, 443
Mayer, P., 432, 443
Mayetiola destructor, distribution, 368;
evaporation on, 371; longevity, 377;
losses through, 410; moisture on, 365
May fly, male genitalia of, *65; wings, *56
McAtee, 461
McColloch, 359, 367, 368
McCook, on ants, 291, 294, 295, 296, 297,
466
McDermott, 449
McEwen, 311
Mclndoo, 90, 445, 446, 470
Mealworm (see Tenebrio).
Meconium, 152
Mecoptera, defined, 17; origin, 24
Media, *54, 55
Median segment, 44, 61
Meek, 436
Megackile, hairs of, *68
Megalodacnc, antenna of, *32
Meganeura, 344
Megarhyssa,* 272
Megilla (see Ceratomegilla).
Melander, 426, 467
Melanism, 180
Melanoplus, alimentary tract of, *io2;
facets, *3o; genitalia, *6y; mandible,
*36; respiration, 122; skull, *29
492
INDEX
Melanotus, larva of, *i42
Meldola, 460
Melissodes, 225
Melnikow, 451
Melo'e, antenna of, 2,3', hypermetamorphosis,
156
Melolontha, male reproductive system,
*i24; olfactory pits, 88
Mendelism, 209
Menopon, *i2
Mentum, *35, 37
Merriam, on life zones, 332, 471, 472
Merrifield, 457, 458
Merrill, 425
Mesenchyme, *i36
Mesenteron, *io2, *io3, *io4, 136
Mesnil, 465
Mesoderm, 130, *i36
Meso-entoderm, *i3i
Mesothorax, 44
Metabola, 140
Metallic colors, 173
Metamorphosis, defined, 137; external, 137;
internal, 160; significance, 159; sys-
tematic value, 24
Metatarsus, *2 28
Metathorax, 44
MetschnikoflF, 446, 451, 454
Miall, on chitin, 66; muscles, 78, 431, 435,
442, 450, 454, 456
Miaslor, paedogenesis of, *i28
Michels, 442
Michelson, 173, 174
Microcentrum, stridulation of, 92, *93
Microphaga, 373
Micropteryx, mouth parts of, 40
Micropyle, 129, 141
Mid intestine, *io2, *io3, *io4
Milkweed, pollination of, 221, *2 22
Mimicry, 201; evolution of, 208
Minot, 440
Miocene insects, 341, 345
Mitchell, 465
Moisture, 364; its effects on activity, 365;
aestivation, 366; coloration, 178; eclo-
sion, 365; hibernation, 365; metabo-
lism, 364; mortality, 365; oviposition,
36s
Molanna, *i7
Moles, insectivorous, 236
Moller, on leaf-cutting ants, 295, 462
Mollock, on vision, 99
Molting, 144, 359
Molts, number of, 144
Moniliform, *3,2
Mononychus, 226
Monophagous, 373
Mordella, facets of, 31
Mores, 393
Morgan, C. Lloyd, 207, 468, 469
Morgan, H. A., 426
Morgan, T. H., 377, 469, 474
Morpho, scales of, 70, 172
Morrill, 354
Morse, A. P., 396, 397, 472, 474
Mosaic diseases, 319 ~
Mosquito, antennae of, *34; hearing, 94;
hibernation, 311; locomotion of larvae,
167; in relation to malaria, 248, 250;
mouth parts, *4i; respiration, 169;
tropisms, 311
Moulton, 461
Mouth parts, dipterous, *4i; hemipterous,
*39; hymenopterous, *42; lepidopter-
ous, *4o; mandibulate, *35; orthopter-
ous, *35; suctorial, 38
Muir, 23
Miiller, F., on mimicry, 204; wings, 53;
460
Muller. H., 462
Miiller, J., mosaic theory of, 98, 443
Miillerian mimicry, 203, 204
Murray, 471
Miisca, egg of, *i39; facets, 31; fungus of,
*2i8; molts, 145; oviposition, 365;
ovum, *i29; in relation to t>'phoid
fever, 257, 258, 259
Muscidae, cardiac valve of, *io4; imaginal
buds, *i6i
Muscles, circular and longitudinal, ro6; of
cockroach, *53, *77; of leg, *sy, num-
ber, 77; structure, *78; of mng. *so
Muscle-tension theory, 311
Muscular, power, 79; system, 77
MiUilla, stridulation of, 92
Muttkowski, 456
Mycetophaga, 374
Myrientomata, 6, *7
Myriopoda, 5
Myrmecocystus, 295
Myrmecodia, 232
Myrmecopkana, mimicry, by, *205
Myrmecophilism, 297 . '
Myrmedonia, 300
493
Myrmeleon, digestive system of, *io3; pre-
daceous, 270; silk glands, 77
Myrmica, *2gg
Mystacides, androconia of, 72
Nagana, 263
Nagel, 444
Nearctic realm, 331
Necrophagous, 373
Necrophorus, 236, 276
Needham, 54, 104, 424, 438, 447, 456,
462
Nelson, 453
Nemobius, leg of, *5o
Neotropical realm, 331
Nepa, respiration of, 169
Nephrocyte, 1 10
Nerves, of head, 81, *82; structure, *8i
Nervous system, 80; development of, 133,
*i3S
Nervures, 54
Neuration, *54, *55, *56
Neuroblasts, *i35
Neuromeres, 44, 134; of head, *43, So
Neuroptera, defined, 17; metamorphosis of,
24, *i43
Newbigin, 458, 460
Newcomer, 362
Newell, A. G., 440
Newell, W., 426
New Mexico, insect communities in, 399
Newport, on metamorphosis, 162; muscles,
78; 435, 441, 442
Newton, 442
NicoUe, 267
Noguchi, 255, 256
Northrop, 373, 476
Notolophiis, olfactory organs of, 89
Notoneda, *i66; locomotion of, *i66; res-
piration, 169
Notum, 45
Novius, 275, 412, 428
Nucleolus, 129
Number of insects, 27
Nuttall, 464
Nymph, 139
Oaks, insects of, 212, 410
Oberea, eyes of, 30
Obtect pupa, *i47
Occipital foramen, 29, *30
Occiput, 29
Ocelli, *3i; structure of, 95; vision bv,
96
Ockler, 437
Ocular, neuromere, *43; segment, 44
Odonata, abdominal segments of, 60; copu-
lation of, 65; defined, 14; ocelli, 31;
origin, 23; spiracles, 60
Odors, 73; efficiency of, 246
Odynertcs, 225
(Ecanlkus, abdominal appendages of, 61,
*i33; embryo, *i33; stridulation, 93
(Ecophylla, 291
(Edipoda, dorsal vessel of, *iio
(Eneis, distribution of, 325
(Enocytes, *ii4
(Esophageal commissures, *82
Esophagus, *io2, *io3, *io4
(Estridae, 234
O'Kane, 426, 477
Olfactory organs, 87, *88, *89
Oligocene insects, 341
Oligophagous, 373
Oligotoma, *ii
Ommatidium, *97, *98
Onthophagus, mandible of, *t,6
Onychophora, 2. *3
Ophthalmia, 269
Ore hell mum, stridulation of, 92
Orders of insects, 7, *25
Oriental realm, 332
Origin of arthropods, *8; of insects, 6
Oroya fever, 269
Orthoptera, abdominal segments of, 60;
defined, 9; ecological succession, 408;
origin, 22; stridulation, 92, *93
Osborn, 426, 477
Osburn, 384, 386, 387, 456
Osmeterium, *74
Osmia, 225
Osmoderma, cocoon of, 148
Osten-Sacken, 440
Ostium, *i09, *iio
Oudemans, 450
Oustalet, 455
Ovaries, 123, *i26
Ovariole, 125
Oviducts, 125, *i26
Ovipositor, 62, *63, *67
Ovogenesis, 129
Ovum, of Musca, *i29; Vanessa, *i2 7
Ox-warble, *i42, 235
494
Paasch, 443
Packard, on Anophthalmus, 100; Arthro-
poda, 7; classification, 7; Mantispa,
143; olfactory pits, 88; relationships of
orders, 22; segmentation, 27; types of
larvae, 142; wings, 53; 423, 427, 431,
432, 433, 439, 442, 444, 449, 454, 455,
461, 476
Pasdogenesis, 128
Palaearctic realm, 331
Palaoblatlina, *34i
Palaeodictyoptera, 347
Palmen, 449, 450
Palmer, 464
Palpifer, *35, 37, *38
Palpiger, *35, 37, *38
Palpus, *2,S, 37, *38, *40
Pankrath, 444
Panorpidae, 18; legs of, 51
Pantophagous, 373
Papilio, colors of, 179; egg, *i39; facets, 31;
head of pupa, *i47; melanism, 180;
mimicry, 202, 205; osmeterium, *74;
protective resemblance, 196; cenea,
mimicry by, 202, 205
Paraglossa, *s5, 37, *38
Paragnaths, 37
Paralysis, infantile, 269
Paraponyx, *ii9, 170
Paraptera, 46
Parasita, defined. 16
Parasitic insects, 233, 271, 275; in relation
to birds, 245
Parasitism, 235, 271; economic importance
of, 274
Parcohlatta, mouth parts of, *35
Parker, on phototropism, 309, 469
Parks, 354, 475
Parman, 352, 363, 365, 475, 476
Parrott, 424
Parthenogenesis, 127, 216, 286, 290, 358
Passalus, cocoon of, 148; stridulation, 91
Patagia, 45
Patch, E. M., 425
Patten, B. M., 470
Patten, W., 444, 452
Pawlovi, 443
Pawlowa, 448
Payne, 311
Peacock, 437
Peairs, 426, 431, 475, 477
Pea louse (see Macrosiphum).
Peck, W. D., 423
Peckham, on behavior, 316, 318, 319, 466,
467, 469
Pecten, *228
Pectinate, *32
Peciinophora gossypiella, 419
Pedicel, *32
Pediculidae, 234
Pediculus, *i5, 234, 267, 268
Pelocoris, leg of, *5o
Penis, 64, *65, 124
Pepsis, 277
Perez, 455
Pericardial, ceUs, no; chamber, *io9, *i23
Peripatus, characters of, 2, *3, 5; systematic
position, 5
Periplaneta, olfactory pits of, 88
Peripodal, cavity, 161; membrane, 161; sac,
161
Peritrophic membrane, 106
Perla, olfactory pits of, 88
Perlidae, *i3, 14; nymph, *i42; tracheal
gUls, *ii8
Permian insects, 344
Peterson, 371, 437, 476
Petiolata, 19
Pettigrew, 437
Pettit, 426
Petunia, *2 25
Peytoureau, 439, 451
Pflugstaedt, 438
Phagocytes, 114, 160
PhancBus, legs of, 49, *5o
Pharynx, 102
Phasmidas, 10, *i95
Philiptschenko, 44
PhiUips, E. F., 429
Phillips, W. J., 368
Phlebotomus fever, 269
Phormia, antenna of, *32; eyes, *3i; meta-
morphosis, *i38; phototropism, 310
Phosphorescence, 114
Pholinus, luminosity of, *ii5
Photogeny, 114
Photopathy, 307
Photophil, 307
Photophob, 307
Phototaxis, 307
Phototropism, 306
Photurts, 116
Phragmas, 46, *48
Phthirius, 234
INDEX
495
Phyciodes, coloration of, 178, *i82
Phylloxera, 350, 410, 416
Phylogeny, 5, *8, *2$
Phytonomus, spread of, 338
Phytophaga, *i9
Phytophagous, 373
Pictet, on coloration, 176, 179
Piepers, 460
Pierce, 24, 157, 354, 360, 368, 375, 376, 378,
434, 463, 466
Pieris, color sense of, 100; dispersion, 322;
.fat-cells, *ii3; imaginal buds, *i62;
olfactory organs, *9o; scale, *6g; napi:
temperature experiments on, 182; pro-
todice: sexual coloration of, *i84;
rapa: androconium of, *7i; developing
wing, *i63; distribution, 338; eggs,
*i4o; food plants, 213; hair, *68; larval
tissues, *ii3; pupal coloration, 177;
wing vibration, 59; xanthodice, distri-
bution of, 322
Pigmental colors, 174
Pigments, of eyes, *96, *97, *98, *99; nature
of, 175; of Pieridc-e, 175
Pilifers, *4o
Pimpla, 274
Pine, insects of, 212
Ping, 476
Pinguicula, 216
Pink boll worm {set PecHnophora).
Placodeum, *85
Plague, 260
Planta, *2 28
Plant lice (see AphididcB).
Plants, diseases of, 218; insectivorous, 216;
insects in relation to, 212
Plasma, no
Plasmodium, 248
Plateau, on color sense, 100; muscular
power, 79; respiration, 123; 441, 444,
446, 449, 468
Platephemera, *342
Platheniis, abdominal appendages of, *66;
antenna, *32
Plalygaster, hypermetamorphosis of, 146,
*IS8
Platypsyllus, 234
Platyptera, defined, 10; origin of, 22, *2$
Plecoptera, defined, 14, *i3; nymph, *i42;
origin, 22, *25
Pleistocene insects, 341
Pleurites, *45, *47
Pleuron, 45
Plotnikow, 441
Pocock, 432
Podical plate, *()^
Podisus, egg of, *i39; predaceous, *27o
Pcecilocapsus, color changes of, 190
Pogonomytmex, 297
Polar bodies, *i29
Poletajew, 449, 455
Poliomyelitis, 269
Polistes, behavior of, 316, 321; habits, 288;
wing vibration, *58
Poliles, on Iris, *226
Pollenizers, insect, 225
Pollination, 219, 225; of Iris, *22o; milk-
weed, 221, *222; orchids, 221; Yucca,
222, *224
Pollinia, *22 2
Polyhia, 287
Polyembryony, 136
Polyergus, 294
Polygoneutic, 182
Polygonia, dimorphism of, 180; egg, *i39
Polymorphism, 289
Polynema, 158
Polyphagous, 373
Polyphemus (see Telea).
Polyphylla, assembling of, 90
Polyrhachis, 291
Pomace flies (see Drosophila).
Pompilus, behavior of, 316, 319
Popillia japonica, 418
Porthetria dispar, damage by, 416; distribu-
tion by winds, 368; gynandromor-
phism, *i28; tracheoles, *i2i
Postclypeus, 29
Postgense, 29
Postscutellum, *45, *46
Potato beetle (see Leptinolarsa).
Pouchet, 468
Poulton, on adaptive coloration, 206, 207,
209; on colors of larvas and pupae, 177;
454, 457, 458, 459, 460, 461
Powell, 139, 455
Pratt, 454, 455
Precipitation, 366
Predaceous insects, 233, *27o; in relation
to birds, 245
PreU, 434
Premandibular, appendages, *i32; segment,
*43, 44
Pressure, 363
496
INDEX
Pricerj 467
Primitive insects, 20
streak, 130
Primordial insect, 21
Priomis, assembling of, 91; eggs, 141
Proboscis, *40
Procephalic lobes, *i32, *i33
Prochnow, 438, 445
Proctodaeum, *io2, 104, 131
Proctotrypidae, 27, 274
Prodoxus, 224
Prodryas, *346
Prognathous, 11
Promethea (see Callosamia).
Pronotum, *46
Pronuba, *223, *224
Propodeum, 44
Propolis, 283
Prolapteron, 6
Protective, adaptations, 245; mimicry,
*20i, 206; resemblance, *i94, 198
Prothorax, 44
Protocerebrum, 80, 135
Protoparce, head of moth, *4o; larva, *si;
moth, *225; parasitized larva, *273
Protura, 6, *7
Proventriculus, *io2, *io3, *io4
Pseudocercus, *6i, 62, *65
Pseudocone, *98
Pseudomyrma, 230
Psocidae, *i2
Pteromalus, oviposition of, 376
Pteronarcys, *i3; tracheal gills of, 119
Pterygota, 9
Ptilodadyla, antenna of, *32
Pulvillus, 48, *5i
Punktsubstanz, 81
Punnett, 209, 461
Pupfe, 137,-146; emergence of, 152; protec-
tion, 148; respiration, 147
Pupal stage, significance of, 159, 162
Puparium, 147, 372
Pupation of a caterpillar, 147, *i49
Putnam, on habits of Bombus, 287
Pyloric valve, 104
Pyrausta nubilalis, spread of, 418
Pyrophila, thigmotropism of, 304
Pyrophorus, luminosity of, 115
Pyrrharctia (see Isia).
Quaintance, 359, 366, 372, 428
Quaternary insects, 346
Quayle, 425
Quedkis, 300
Queen, honey bee, *282; termite, *278
Radius, *54
Rddl, 469
Rainfall, 366
Ranatra, 166; phototropism of, 311; respira-
tion, 169
Rand, 463
Raschke, 449
Rath, vom, on sense hairs, *9o; 444, 445
Rathke, 449
Rationality, apparent, 314; lack of, 321
Rau, 352, 470
Realms, faunal, 328, *329
Reaumur, de, 435
Receptaculum seminis, 125, *i26
Recognition markings, 211
Rectal respiration, 119, 170
Rectum, 105
Recurrent nerve, 81, *83
Redikorzew, on ocelli, *96, 445
Redtenbacher, 437
Reed, on yellow fever, 253, 465
Rees, van, 454
Reichenbach, on ants, 128
Relapsing fever, 267
Relationships, of arthropods, 4, *7; oi
orders, 20, *25
Repellent glands, 73
Replacements, 190
Reproduction, of plant lice, 358
Reproductive system, 123
Respiration, 122, 147, 155
Respiratory system, 116, *ii7
Reticitlitermes, 279, 281
Retina, *g6
Retinula, *g(), *g%
Renter, 445
Rhabdom, *g(), 97, *98
Rheotropism, 304
Rhipiphorus, 156
Rhopalocera, 18
Rhyphus, *5S
Ricketts, 267, 269
Riley, C. F. C, 304, 470, 474, 476
Riley, C. V., on hypermetamorphosis, 156;
losses through insects, 410; pollination
of Yucca, 222; pupation, 147; 377, 4io>
412, 425, 427, 454, 462
Riley, W. A., 139, 465
497
Rimsky-Korsakow, 6, 434
Ritter, 438
Robertson, 462
Robin, food of, 240
Rocky Mountain locust, dispersion of, 322;
as food of birds, 243
Rocky Mountain spotted fever, 269
Rolfs, 426
Rollet, 442
Romanes, on instinct, 317, 468
Rosenau, 269
Ross, on malaria, 250, 464
Rossig, 462
Rostrum, 39
Roziles, *296
Ruggles, 425
Ruland, 444
Sadones, 450, 455, 456
Saliva, of Dytiscus, 107; mosquito, 107
Salivary glands, *io6, *io7
Sambon, on malaria, 250
Samia cccropia, antennas of, *2,y, cocoon,
*i5i; egg, 141; food plants, 213; geni-
talia, *66; head of larva, *74; Malpigh-
ian tubes, *io8; ocelli, *3i; odor, 74,
scales, *7i
Sanderson, 356, 359, 360, 362, 365, 366, 370,
426, 431, 474, 477
Sandias, 466
San Jose scale insect (see Aspidiotus perni-
ciosiis) .
Saprophagous, 373
Sarcolemma, *78
Sarcophaga, nervous system of, *82
Sarcophagous, 373
Satiirma, hairs of, *68
Saunders, 429, 476
Saville-Kent, 472
Scales, arrangement of, *7o; development,
70, *7i; form, *6g, *7i; occurrence of,
69; uses, 70
Scape, *32
Scarabaeidoid larva, 157
Scavenger insects, 236
Schaffer, on scales, 70; 435, 441, 448
Schenk, on sensilla, 84, *85, 89, 445
Schepotiefif, 6, 434
Scheuring, 445
Schewiakoff, 442
Schiemenz, 446
Schimper, 462
32
Schindler, 446
Schistocerca, distribution of, 323, 339; of
Galapagos Islands, 326; isolation, 328
Sckizoneura, wax of, 75
Schizura, protective resemblance of, *io6
Schmidt, O., 454
Schmidt, P., 433, 448
Schmidt-Schwedt, 449
Schneider, A., 450
Schneider, R., 440
Schoene, 424
Schon, 445
Schroder, 436
Schwarz, on distribution, 336, 337; myrme-
cophilism, 300, 471
Schwedt, 455
Sclerite, 28
Scolopendra, *5, 401
Scolopendrella, *6, 21
Scorpion, *2, 401
Scudder, on albinism, 180; coloration, 187;
fossil insects, 341, 345, 346, 347; glaci-
ation, 326; mimicry, 203; Orthoptera
of Galapagos Islands, 326, 328; spread
of P. rapa, 338; stridulation, 92; 443,
457, 471, 473> 474
Scutellum, *45
Scutum, *45
Seasonal coloration, 180
Sedgwick, 433
Segmentation, of arthropods, 27; germ
band, *i3i, 132; head, *43
Segments of abdomen, 60
Seitz, 457, 462, 466, 468, 471
Sematic colors, 210
Seminal ducts, 124; receptacle, 125, *i26;
vesicle, *i24
Semon, 472
Semper, C, on scales, 70
Semper, K., 471
Sempers, 477
Sense organs, 83
Sensilla, 84, *8s
Serosa, *i3i, *i34
Sessili ventres, *i9
Setaceous, *32
Setae, modifications of, 69
Seventeen-year locust, 145
Severin, 359, 371, 470
Sex-determination, 376
Sexual coloration, 184
Shannon, 472
498
INDEX
Sharp, on AUa, 293; Hawaiian beetles, 326;
metamorphosis, 159; 415, 431, 433, 449,
455
Sheath, *64
Shelford, R., 460
Shelf ord, V. E., on chemical conditions, 383;
communities, 393, 397; environments,
388, 389; evaporation, 368, 369, 370,
371; physical conditions, 384; succes-
sion, 404, 406, 407, 408; tension lines,
399; tiger beetles, 174, 175, 183, 189,
350; 459, 472, 474, 475, 576
Sherman, F., Jr., 426
Sherman, J. D., Jr., 386, 456
Shreve, 389, 391, 476
ShuU, 94, 445
Silk, 76
Silk glands, 75, *y6
Silkworm (see Bombyx mori).
Silpha, distribution of, 336
Silurian insects, 341
Silvestri, on Anajapyx, *6; 433, 434
Simmermacher, 440
Simpson, 358
Simulium, 233; respiration, 170
Sinclair, 433
Siphonaptera, *2o; origin of, *25, 26
Sirex, ovipositor of, *64
Sirrine, 424
Sitaris, 156
Size of insects, 27
Skin, 66
SkuU, 28, *29
Skunk, insectivorous, 236
Sladen, 287, 467
Sleep of insects, 352
Sleight, 385, 456
Slingerland, 411, 424, 477
Smell, 87; end-organs of, *88, *89
Sminthurus, *io
Smith, E. F., 219
Smith, J. B., 425, 477
Smith, R. C, 426
Smith, T., 269
Snodgrass, 24, 326, 328, 436, 438
Snow flea, *io
Snyder, 468
Societies, 389
Soil, 348; nutriment in, 351; structure of,
348; temperature, 350
Soldier, ants, 289; termites, *277
Somatic cells, 129
Sorensen, 433
Sounds, 91
Spence, 431, 432
Spermatheca, 125, *i26
Spermatogenesis, 129
Spermatophores, 124
Spermatozoa, 124, *i25
Sperm-nucleus, 129
Speyer, on hermaphroditism, 126
Sphecina, 277
Sphecius, 277
Sphex, *223; behavior of, 316, 318, *3i9
Sphingidae, as poUenizers, 221, *2 25
Sphinx, alimentary tract of, *io4; dispersal,
323; pulsations of heart, 112; trans-
formation, *i63
Spichardt, 450
Spillman, 268
Spines, 69
Spinneret, *74, 75
Spiracles, closure of, *i2o; number, 60, 119
Sbiroholiis, *3
Si^irochata, 267
Spongioplasm, 78
Sporotrichum, 218, 367
Spuler, on scales, 70; 438, 441, 458
Spur, *49
Squama, 54
Squash bug, metamorphosis of, *i38
Stadium, 140
Stagmomantis , leg of, *5o
Standfuss, temperature experiments of, 183,
458
Stedman, 426
Stefanowska, on pigment, 99; 444
Stegomyia, 255
Stellwaag, 438
Stenanima, 292
Stenobothrus, blood corpuscles of, *iio;
stridulation of, 92
Stenodictya, *343, 344
Stephens, 465
Stereotropism, 303
Sternberg, 250, 251, 464
Sternum, *47
Stigmata (,see Spiracles).
Sting of honey bee, *64
Stinging hairs, *73
Stings, efficiency of, 246
Stipes, *35, 37, *38
Stokes, 449
Stomach, *io4
499
Stomachic ganglion, 8i, *8s
Stomatogastric nerve, 8i, *83
Stomodaeum, *io2, 131
Strata, 393
Slratiomys, 360
Straton, 462
Straus-Diirckheim, on muscles, 78; 435, 441
Strength, muscular, 79
Strepsiptera, 17, 137, 157
Stridulation, 92, *93
Strindberg, 453
Strong, R. P., 266
Strottgylonotus, 294
Structural colors, 172
Styloconicum, 84, *85
Stylops, hypermetamorphosis of, 157
Subcosta, *54
Subgalea, *38
Submentum, *35, *38
Suboesophageal ganglion, *8i, *82
Succession, 404; causes of, 404; ecological,
406; of forest communities, 406; geolog-
ical, 404; of Orthoptera, 408; seasonal,
405; of tiger beetles, 407
Suctorial mouth parts, 38
Suffusion, 178
Summers, 426
Superlingua;, 36, *38, *i32, 133
Superlingual, neuromere, *43, 81, 135; seg-
ment, 44
Supracesophageal ganglion, 80, *82
Suranal plate, 62, *67
Surface film, 168
Suspensor, 125
Suspensory muscles, *iio
Swarming, 286
Swenk, 426
Symbiosis, 299
Symons, 426
Sympathetic system, *8i, *83
Symphyla, 3, *6
Synchronism, of fireflies, 116
SjTiecology, 348
Syrphidae, silk glands of, 77
Systole, III
Tabanidae, 233 •
Tabanus, nervous system, *82; olfactory
organ, *89
Tachardia, 75
Tactile hairs, 69, 84, *8s
Tanidia, *i2 2
Tarantula, 401
Tarsus, *48
Taschenberg, 430
Taste, 84; end-organs of, *86, *87, *88
Taxis, 302
Tegmina, 53
Tegulae, 46
Telea polyphemus, cocoon of, 148; eclosion,
152; larval growth, 144; silk glands, 75;
spinning, 151
Teleas, 158
Telson, 60
Temperature, 352; acclimatization to, 360;
on activity, 353; on coloration, 182; on
distribution, 362; on hibernation, 361;
on incubation, 358; limits, 352; on
reproduction, 358; of soil, 350
Temperature-constant, 355
Tenebrio molitor, development, 359, 360;
incubation, 359; metabolism, 370
Tenent hairs, *72
Tension lines, 399
Tenthredinidae, larval legs of, 51
Tenthredopsis, larva of, *i42
Tentorium, 29, *3o
Terebrantia, *i9
Tergites, *45, *46
Tergum, 45
Termites, American species of, 279; archi-
tecture, *28o; classes of, *277; "com-
pass," *28o,- food of, 279; mandibles,
*36; origin of castes, 279; queen, *278;
ravages, 281
Termitidae, 11
Termitophilism, 281
Tertnitoxinia, 126, 127
Termopsis, 278
Tertiary insects, 341, 345
Testes, *i24
Tetralonia, 225
Tettigoniidae, 10; ovipositor, *6y, spermato-
zoon, *I25
Texas fever, 269
Thalessa (see Megarhyssa) .
Thanaos, androconia of, 72; claspers, 65
Thayer, 461
Thaxter, on Empusa, 217, *2i8; 462
Thelen, 449
Theobald, 477
Thermotropism, 312
Thigmotropism, 303
Thimm, 465 ,
500
INDEX
Thomas, 424, 427
Thompson, C. B., 443, 468
Thompson, S. M., 463
Thorax, differentiation of, 44; parts of, *45;
sclerites of, *45, *46, *47
Thread-press, *76
Thyridopteryx, eggs of, 141
Thysanoptera, *i4, 15; origin of, 22,, *2$
Thysanura, 8, *9; abdominal segments, 60;
primitive, 20
Thysanuriform, 24, *i42, *i43, 160
Tibia, 48, *49
Tiger beetles (see CicindelidcB) .
Tillyard, 438, 476
Tipula, *2o
Titanophasma, 27
Toad, insectivorous, 236
Tongue, 37
Torre-Bueno, 475
Touch, 84
Tower, D. G., 437
Tower, W. L., on color patterns, 186;
cuticular colors, 175; distribution of
Lcptinoiarsa, 336; folding of wing, 56,
*57; hibernation, 365; integument,
*67; origin of wings, 53; structural
colors, 173; 441, 459, 472
Townsend, A. B., 448
Townsend, C. H. T., 426
Toxoptera graminum, development of, 356,
364; distribution of, 368
Toyama, 451
Tracheae, development of, 135, *i36; dis-
tribution, *ii7, *ii8; structure, *i2i
Tracheal gills, *ii8, 169
Tracheation, types of, 117
Tracheoles, *i2i, 122
Trelease, 462
Tremex, *i9
Trench fever, 268
Triassic insects, 345
Trie kins, 225
Trichodeum, 84, *85
Trichogen, *68, 69, *7i
Trichogranima, 274
Trichoptera, 18, *i7; origin of, *25; silk
glands, 77
Trichopterygidae, size of, 27; 273
Trimen, on dispersal, 323; on P. ccnca, 202,
205; 459, 460
Trimerotropis, protective resemblance of,
196, *i97
Trimorphism, 180
Triphleps, egg ofj *i39
Tritocerebrum, 80, 135
Triungulin, 156, *i57
Trochanter, 48, *49, 50
Trochantin, 48
Trogoderma, 2,11
Tropcca luna, cocoon of, 148
Trophallaxis, 301
Tropical region, 335
Tropidacris, 27; respiratory muscles of, *i23
Tropisms, 302
Trouessart, 471
Trouvelot, on cocoon-spinning, 151; eclo-
sion, 152; larval growth, 144; 453
Trypanosomes, 261, *262, *264
Trypanosomiases, 261, 263, 264
Tryphana, 116
Tsetse fly, 262, *263
Tuberculosis, 269
Turner, loi, 445
Tutt, 472
Typhoid fever, 257
Typhus, 266
Uhler, on distribution, 337
Uichanco, 358
Underbill, 464
Urech, 457, 458
Uric acid, 108; as a pigment, 175
Urosternite, 60
Urotergite, 60
Useful insects, 411
Utricularia, 217
Uzel, 453
Vagina, 125, *i26
Valette St. George, la, 450
Vanessa, development of scales of, *7i ; head
of butterfly, *4o; antiopa: 246; photo-
tropism, 309; atalanla: color change,
190; cardui: dispersion, 322, 326; geo-
graphical variation, 328; polychloros:
coloration, 179; melanism, 180; urticce:
coloration, 176; melanism, 180; tem-
perature experiments, 183
Variation in coloration, 188, *i9i, *I92
Variations, 190
Vas deferens, *i24
Vayssiere, 447, 449, 455
Vedalia (see Novius).
Vegetation map of U. S., *39i
INDEX
Veins, *54
Velum, *228
Venation, *54
Ventral sinus, no, *i23
Ventral tube, 62
Ventriculus, *io4
Verhoeff, 438, 439, 440, 466
Vernon, 459
Vertex, 28
Vervvorn, on phototropism, 308; 469
Vespa, nests of, *288; olfactory organ, *89;
sensillum, *85; taste cups, *87; tongue,
*86
Vespidas, 287
Vestal, 394, 475
Viallanes, 435, 442, 448, 454
Vinal, 450
Vision, 95
Vitelline membrane, *i29
Vitreous body, 95, *96
Voliicclla, mimicry by, *2io; predaceous, 271
Voss, F., 438
Voss, H. v., 459
Wagner, F. v., 459
Wagner, J., 433
Wagner, N., 450
Wahl, 455
Walker, E. M., 434, 435
Walker, J. J., 456
Walking, 51
Walking-stick, *i95
Wallace, on mimicry, 203; 459, 460, 471
Walsh, on losses through insects, 410; 424
Walter, on mouth parts, 40; 436
Walton, 428
Warming, 474
Warning coloration, 199
Washburn, 425, 464
Wasmann, on myrmecophilism, 297; 466,
469, 470
Wasps, 287
Wasteneys, 470
Watase, 444
Water, 382; circulation of, 384; contents
of, 383; depth, 386; pressure, 385; of
soil, 350; temperature of, 385; vegeta-
tion of, 386
Watson, 474
Wax, 413
Wax, glands, 74; pincers, *2 28,^229
Webb, 429
Webster, F. M., on dispersal, 323, 335, 338,
368; losses through insects, 410; 425,
460, 462, 466, 471, 472
Webster, R. L., 426
Wedde, 436
Weed, C. M., on birds in relation to insects,
242, 243, 245; 426, 464
Weinland, 444
Weismann, on imaginal buds, 161; instinct,
317; temperature experiments, 182;
451, 453, 457, 458, 459, 460, 469
Weiss, 156, 311, 475
Welch, 456
Welles, 447
Wesche, 437
West wood, on Brachinus, 73; 431, 432
Wheeler, on ants, 289, 297, 320; Malpighian
tubes, 108; protective coloration, 178;
trophallaxis, 301; tropisms, 302, 303,
305, 306, 311; 439, 447, 448, 452, 453,
467, 468, 469
White, F. B., 455
Whitman, 469
Whymper, on distribution, 322; 472
Wickham, 347
Wielowiejski, von, 448, 450
Wilcox, 451, 463
Wilde, 446
Wilder, 267
Will, F., on taste, 85; 444
Will, L., 450, 452
Williams, C. B., 434
Williams, T., 449, 455
Wilson, 453
Wilt, cucurbit, 219
Wind, distribution by, 323, 368
Wings, 53; folding of, 56, *57; modifications
of, 53; muscles of, *59; venation, *54;
vibration, 57, *58, 91
Wistinghausen, von, 449
Witlaczil, 440, 447, 452, 454
W^odsedalek, 377
Wollaston, on beetles of Madeira Islands,
326
Woodward, 453 '
Woodworth, 425, 438
Worker, ant, 289; bee, *282, 286; termite,
277, *278; wasp, 288
Xanthophyll, as a pigment, 176, 193
Xenoneura, *342
Xiphidium, stridulation of, 92
502
INDEX
Yapp, 369 Z ait ha, 171
Yaws, 269 Zander, 440
Yellow fever, 252 Zeuzera pyrina, 419
Yolk, *i29, *i3o Zittel, von, 433
Yothers, 361, 377 Zones, life, *2,3z
Young, R. T., 461 Zoraptera, 12, 22
Yuasa, 437 Zorotypus, 12, 22
Yucca, pollination of, 222, *2 24 Zugmayer, 461
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